The coast is a zone of intense industrial and economic activity, due to a combination of high population density, resource availability and access to shipping for the transport of goods. Historically, regulations for discharging pollutants into coastal land and marine environments were lax or absent, causing legacy issues of contamination that are still borne today (e.g. contaminated sediments in urban estuaries). More recently, improved regulation and monitoring has led to reductions in the impacts of some industries on the coastal environment.

The overall impact of industry pressures on the environment depends on both their scale and intensity. Pressures from industry can be from point sources and highly localised, such as a mine or gas plant, or diffuse across large areas, such as run-off from coastal farms into the Great Barrier Reef. Although some industries inflict severe destruction to certain areas, the total damage from localised impacts may be less, relative to other pressures, than is perceived.

Indigenous people’s exposure to inshore and offshore marine industries is growing and intensifying in Australia. Alongside this are growing native title claims made over sea Country. Co-existence between companies, governments and Indigenous people is needed. In an era of heightened awareness of environmental protection and sustainability, the legitimacy of industry operations in many sectors, including marine industries, is being increasingly questioned by the public (Dare et al. 2014, Kilian & Hennigs 2014). Industries must now work harder to obtain the ongoing broad acceptance of the community to remain an ongoing business.

Cultural disparities between Indigenous and non-Indigenous people can be resolved by genuine negotiation. Joint arrangements need a mechanism for including Indigenous views more systematically in processes of negotiation and agreement-making. More industries need to face the negotiation arena rather than avoid debates, especially since businesses operate in an environment of contested values. By disregarding the values of the societies and cultures in which they operate, businesses run the risk of boycotts, and legal and legislative action that can put them out of business or seriously jeopardise ongoing business.

Traditional Owners within the ‘blue economy’ industry sector face significant challenges due to the weakening of their Indigenous cultural legitimacy by poor inclusion, and missed benefits due to exclusion from – or under-resourcing of – participatory processes. To capitalise on blue economy industry opportunities, resources are needed to develop significant Indigenous-led blue industries. The Indigenous Land and Sea Corporation is investing in unlocking the Indigenous estate through its Indigenous agribusiness strategy. There are also emerging markets for environmental services in sea Country through restoration and management of invasive crown-of-thorns starfish. Traditional Owners are looking for government support and enhancement of emerging markets, and to avoid governments becoming market gatekeepers or destroying such markets through ill-considered regulatory action (Dale et al. 2018).

Assessment Pressures associated with industry
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Somewhat adequate confidence
Indigenous assessment
2021 Assessment graphic for an assessment conducted by Indigenous community members, showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.

Most industry pressures are considered low impact and stable, largely due to their localised impacts. Nutrient pollution, artificial structures and contamination in urban estuaries are all considered high impact, though nutrient pollution is improving. The pressure from artificial structures is considered to be increasing due to the expansion of foreshore developments.
The Indigenous assessments for the state of industry pressures found 1 pressure has a very low impact, 2 have a low impact and 2 have high impacts; the trends for all pressures are stable.
Local government assessments (see Approach) show that the presence and intensity of industry pressures vary around Australia, but tend to be greatest near major cities.
Related to United Nations Sustainable Development Goal targets 12.4, 14.1, 14.4, 14.6

Assessment Nutrient pollution
2021 Assessment graphic showing that pressures are high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation is improving.
Adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

Nutrient pollution continues to cause significant harm in Australia. The trend is improving, but emerging issues such as organic loads remain a concern.
The Indigenous assessment for some regional areas was high, with a stable trend.

Assessment Contaminants in urban estuaries
2021 Assessment graphic showing that pressures are high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation is stable.
Limited confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

The state of urban estuaries is generally very poor due to legacy and contemporary contamination. The expansion of coastal cities and port developments is likely to continue the degradation of Australia’s coastal and estuarine ecosystems.

Assessment Mining and energy production
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Somewhat adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

Locally significant pressures are focused around export facilities and ports rather than extraction operations, and pressures levelled off as the mining boom finished.
The Indigenous assessment for some regional areas was low, with a stable trend.

Assessment Artificial structures
2021 Assessment graphic showing that pressures are high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation is deteriorating.
Adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation was deteriorating.

Pressure is increasing with sea level rise, coastal development and demand for supporting infrastructure such as ports and marinas, particularly around urban estuaries.

Assessment Aquaculture
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Somewhat adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation was stable.

Pressure is increasing as industry grows, but most impacts are small in spatial scale.
The Indigenous assessment for some local areas was very low, with a stable trend.

Assessment Desalination
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Somewhat adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The trend was unclear.

At current operating levels, desalination is a relatively low-intensity and localised pressure.

Assessment Dredging
2021 Assessment graphic showing that pressures are low, meaning they minimally degrade state of the environment, over a small extent and/or with low severity. The situation is stable.
Limited confidence

Dredging is a consistent pressure, particularly in the north of Australia, but impacts are relatively localised and generally low outside the dredging footprint.
The Indigenous assessment for some local areas was very low, with a stable trend.

Assessment Flow regimes
2021 Assessment graphic showing that pressures are high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation is improving.
Adequate confidence
Assessment graphic from 2011 or 2016 showing that pressures were high, meaning they moderately degrade the state of the environment, over a moderate extent and/or with moderate severity. The situation was improving.

Reduced and altered flow regimes are driven by regulation and climate change. Environmental water flows are reducing the negative impacts of regulation.

Nutrient pollution

Nutrients (nitrogen, phosphorus, carbon, silica) support the micro- and macroalgae, seagrasses and mangroves that in turn support coastal productivity. Coastal waters around Australia are typically well illuminated, low in nutrients, and support moderate abundances of phytoplankton, zooplankton and fish.

However, nutrient and organic pollution from human sources may lead to excessive growth of nuisance or harmful algae (Davis & Koop 2006), and in extreme cases, deoxygenation of the water. These in turn affect levels and life processes of phytoplankton, zooplankton and fish. Nutrient and organic pollution are particularly important issues for the naturally nutrient-poor waters of Australia, and can cause large-scale disruption in estuaries and sheltered coastal waters.

All states recognise the need to manage nutrient pollution from wastewater treatment plants (WWTPs) and industry, and report substantial efforts to manage urban and rural run-off (Table 5). However, the success of these efforts varies considerably between regions.

Nutrient sources

Coastal nutrients can come from natural ocean upwelling, or from human (anthropogenic) sources, such as diffuse-source catchment run-off or discharge from point sources (e.g. effluent from industrial activities, WWTPs and aquaculture) (Pritchard et al. 2003). Estuarine and sheltered coastal waters in their natural state are clear and low in nutrients because of Australia’s generally poor soils (Harris 2001), but these waters are potentially strongly influenced by run-off from catchments and point sources (BMT WBM 2017, Bugnot et al. 2018).

The risk of nutrient pollution is highly dependent on input loads. Algal growth in estuaries is not a simple linear response to nutrient inputs (Davis & Koop 2006), but a complex interaction between nutrients, temperature, stratification, internal recycling of nutrients and containment of receiving waters.

Algal growth and eutrophication (excessive enrichment leading to oxygen depletion) are the main issues in estuaries and some enclosed coastal waters. The primary drivers of this are increased intensity of rural and urban catchment land use, WWTP and industrial discharges, and, in South Australia and Tasmania, organic loads from finfish aquaculture. Nutrient pollution from coastal land use has been identified as a major stressor for the Great Barrier Reef. There is increasing concern about organic loads from finfish aquaculture in sheltered waters.

Oxygen depletion is driven by bacterial decomposition of organic matter, either in the water column or in benthic sediments. Organic enrichment can result from collapsing algal blooms, as well as from direct inputs (e.g. discharge by industry, aquaculture). Nutrient pollution is also linked to other ecological disturbances, for example, along the Great Barrier Reef (Waterhouse et al. 2012) (see case study: Terrestrial chemical pollutants, particularly pesticides, entering the Great Barrier Reef lagoon).

The extensive fires in eastern and southern Australia in summer 2019–20 transformed catchments. Removal of vegetation and deposition of partially burnt vegetation has exacerbated the risk of diffuse-source inputs of nutrients and carbon following rain. Stratification, bottom water oxygen depletion and delayed algal growth response to nutrient and carbon loads following run-off after bushfires have been observed in some New South Wales estuaries.

States and the Northern Territory generally have large-scale integrated plans to address urban and rural run-off, particularly in identified problem sites. These are supported by monitoring programs to demonstrate benefits, though these is a significant lag time before ecological and environmental benefits will become evident.

The Reef 2050 Water Quality Improvement Plan is a joint commitment of the Australian and Queensland governments that seeks to improve the quality of water flowing from catchments adjacent to the Great Barrier Reef. While there has been encouraging progress, with improved land management practices leading to pollutant reductions, the overall marine condition remained poor in the 2019 Reef Water Quality Report Card.

In New South Wales, however, the statewide estuary condition monitoring program that has run for 14 years shows that in the first 3 years (2007–10), 57% of estuaries had low algal abundance, but in 2017–19, 75% had low algal abundance. This indicates a possible long-term trend of improving condition.

Table 5 Drivers, issues/state, response and outcomes of nutrient pollution, by state






New South Wales

Rural and urban catchment land-use intensification, WWTP discharges and modifications to estuary mouths

Pelagic and benthic algal blooms

The NSW MEMS is a comprehensive approach to address the main threats, through refinement of legislation and regulation, improved planning practices (e.g. risk-based assessment of impacts of development on ecological outcomes), industry codes of best practice, on-ground restoration works, research, and comprehensive monitoring programs.

The result is improved understanding of the complex interactions between nutrient loads and flow in the Hawkesbury River.

The implementation of the MEMS is on track and outcomes will be assessed after 5 years.

Hawkesbury River research is driving revision of allowable nutrient loads to minimise threat of harmful algal blooms.


Diffuse loads of nutrients to the Great Barrier Reef

Point discharges, principally WWTPs

Impacts on corals and associated ecosystems

Pelagic and benthic algal blooms

Reductions in agricultural and urban run-off. The Reef 2050 Water Quality Improvement Plan and, more recently, the Reef Protection Regulations were introduced to reduce nutrient, sediment and pesticide loads discharging to the Great Barrier Reef, through improved land management practices.

Extensive modelling and monitoring of loads and system responses. Most WWTPs in Queensland have been brought up to best management practice.

Difficult to measure change due to extreme variability in wet seasons from one year to the next. It may take decades before any significant change is apparent.

The outcomes from investments in improved management practices to reduce anthropogenic nutrient pollution to the Reef are tracked through the Paddock to Reef Integrated Monitoring Modelling and Reporting Program. Due to interannual variability from climate and the expected lag time before a response can be measured, modelling is used to estimate improvements from the implemented changes in land management practices

Improvements in treatment led to nutrient loads from sewage treatment plants being reduced, by over 70% in many waters, with commensurate reductions in impacts on receiving water.

Blooms of phytoplankton or macroalgae related to point discharges are now rare, and if they do occur are of limited extent.

South Australia

Nutrient loads from urban and rural run-off, point discharges from industry and WWTPs

Climate change – sea surface temperatures

Organic loading from finfish aquaculture

Eutrophication and loss of seagrass

Changes to benthic habitats

Reductions in nutrient-rich discharges along the Adelaide coast have occurred through government and community initiatives. Sludge discharges to marine waters have been eliminated and substantial reductions in effluent from WWTPs have been achieved.

A cooperative regulatory relationship between the Whyalla steelworks and the Environment Protection Authority has improved treatment and assimilation of the nutrient discharges.

In Adelaide coastal waters, ambient nutrient levels have been reduced and seagrass is recovering; there has been almost 800 hectares of seagrass gain in the offshore waters throughout the southern part of the coast. However, the inshore margin is still impacted by sediment discharges. Small-scale physical transplantation has shown some success, with cores expanding to form extensive meadows of Posidonia seagrass.

In Spencer Gulf, the overall condition is fair to good, but the condition declines to poor in the north of the gulf. The pressure throughout the gulf is increasing with proposed expansion in sea cage aquaculture, the major nutrient contributor.


Nutrient loads from urban and rural run-off, point discharges from industry and WWTPs

Organic loading from finfish aquaculture

Algal blooms and eutrophication

Anoxia resulting from oxygen demand driven by benthic decomposition of direct organic loads

Long-term and publicly available nutrient monitoring programs focus on the Tamar estuary in the north, both the Derwent Estuary and Storm Bay in the south, and Macquarie Harbour in the west. More recent monitoring programs are underway in areas potentially subject to increased intensification of marine finfish aquaculture, namely in the D’Entrecasteaux Channel, Port Arthur and Oakhampton Bay. Targeted maintenance programs aiming to reduce nutrient discharge from WWTPs throughout the state successfully decreased nutrient loads from some plants.

The Environment Protection Authority recently reduced the permitted finfish production load.

Decrease in nutrient loads from WWTPs has been detected in some ambient monitoring programs of the receiving waters. The prognosis is towards gradual nutrient load reduction, at least with respect to municipal wastewater treatment. However, further nutrient reduction requires significant funding and will depend on prioritisation of effort within the relevant regulatory departments and industry responsible.

High-intensity monitoring of potential finfish aquaculture impacts is underway throughout the state, but the link between some monitoring results and management decisions is evolving.


Catchment land use (including urbanisation of coastal regions), altered flow regimes, and modifications to estuary mouths

Pelagic and benthic algal blooms

Low dissolved oxygen

The Victorian IEC framework was developed to address a lack of consistent and systematic measurement of estuarine condition in Victoria.

Port Phillip Bay’s plan to manage future challenges to the health and resilience of the bay is currently being implemented. The 3 goals for the bay are improved stewardship, water quality and marine biodiversity. The plan includes audits and remediation of stormwater infrastructure, upgrades of WWTPs, litter reduction, and monitoring and modelling to assess volumes of nitrogen and other pollutants and calculate cumulative annual loads discharging into the bay.

Victoria’s first IEC is due for reporting in 2020–21 and will provide information about the overall environmental condition of Victoria’s estuaries that will guide state policy and regional investment programs.

Western Australia

Nutrient and organic loads from intensification of agriculture and urban development, point discharges from industry and WWTPs

High loads

Reduced rainfall and riverflow

All exacerbated by heavily drained catchments, high water tables and very low nutrient retention in soils

Algal blooms and fish kills from low oxygen

Comprehensive response across most ‘at-risk’ estuaries through the Regional Estuaries Initiative and now Healthy Estuaries WA.

Recently announced the Peel Harvey Estuary Protection Plan.

Successes have included engaging the fertiliser and dairy industries in a partnership approach to match fertiliser use to agronomic need and to improve effluent management from dairy farms. More than 500 farmers participated in the past 4 years.

The Peel Harvey Estuary Protection Plan is a whole-of-government approach that acknowledges the clear linkage between planning decisions and water quality. Actions will be directed at both reducing nutrients from current practices and minimising nutrient losses from future land-use decisions.

IEC = Index of Estuary Condition; MEMS = Marine Estate Management Strategy; NSW = New South Wales; WA = Western Australia; WWTP = wastewater treatment plant

Note: Contributors include Andrew Moss (Department of Environment and Science, Queensland); Greg Woodward (Department of Environment, Land, Water and Planning, Victoria); Sam Whitehead (Derwent Estuary Program, Tasmania); Sam Gaylard (Environment Protection Authority, South Australia); Malcolm Robb (Department of Water and Environmental Regulation, Western Australia).

Contaminants in urban estuaries

Australian coastal ecosystems are threatened by contaminants released through human activities, such as mining, agriculture, aquaculture, shipping and urbanisation. Types of contaminants include metals (e.g. copper, lead, zinc), nutrients, hydrocarbons and synthetic compounds. There is an ongoing legacy of contamination from past industrial activities in coastal cities. Some of this contamination is biologically benign when bound in sediment, but can impact plants and animals when released once sediments are disturbed. Changes to nutrient cycling due to excess organic material and dissolved nutrients delivered during wet weather can also result in the release of toxic compounds, such as ammonia oxide and hydrogen sulfide.

Contaminants in coastal waterways can affect biodiversity, habitat quality and ecosystem functions (Mayer‐Pinto et al. 2020). Some mobile animals such as fish and crustaceans may avoid pollutant plumes from stormwater inputs by temporarily changing their home ranges. Other aquatic organisms, such as seaweeds and animals that live attached to rocks, are more vulnerable because they cannot move away from a pollution source and may bioaccumulate significant concentrations of pollutants. Even mobile species that behaviourally avoid direct exposure to contamination may be affected if their prey species take up and accumulate contaminants. In stagnant or poorly flushed waterways that are already stressed by legacy industrial contaminants, this risk of exposure is greater because pollutants tend to linger in the water column and become bound to sediments. They then act as a future source of contamination, as well as impacting the already-stressed communities living within these habitats.

While the impacts of many of these contaminants have been studied in isolation, the potential for them to interact with additive or synergistic results requires further investigation (O'Brien et al. 2019). The effects of climate change stressors such as ocean acidification, increased temperature and extreme weather events may also interact with contaminants (Cabral et al. 2019).

Contaminant sources

The primary sources of contemporary contaminants in urban areas are stormwater run-off (with contaminant inputs such as excess metals, organic matter, fertilisers and debris, including microplastics and nanoparticles) and sewage overflows (with inputs such as microbial pathogens, personal care products, pharmaceuticals and excess nutrients). More recently, extensive coastal bushfires followed by large wet weather events have caused ash and debris run-off (Joehnk et al. 2020). Another group of contaminants to receive recent attention are per- and poly-fluoroalkyl substances, used in firefighting foam, which are affecting surface and groundwater near air force bases (see the Inland water chapter).

Contaminant inputs from the 2019–20 bushfires devastated coastal habitats across the country, promoting harmful algal blooms and mass mortalities of fish. Few studies have examined the impact of the toxins generated from bushfires on aquatic organisms, although research to fill these gaps is underway in many states. However, the long-term impacts on coastal environments and estuarine waterways from these fires and subsequent flooding could take many more months or years to be realised. Therefore, management of bushfire-affected catchments requires long-term monitoring of the related impacts to address knowledge shortfalls and support future adaptation and mitigation.

In Sydney Harbour, it has been estimated that more than two-thirds of the pollutants entering the waterway do so via stormwater drains (Freewater & Kelly 2015), creating hotspots of pollution 20 times greater than pre-human disturbance concentrations. Impervious surfaces, which cover 80% of the catchment, increase the volumes of stormwater run-off. The recent threat and risk assessment conducted by the New South Wales Marine Estate Management Authority showed urban stormwater discharge as the second highest threat to environmental assets of the Hawkesbury–Nepean bioregion.

Current urban and port developments in Queensland have increased the sources and diversity of contaminants being released into the coastal environment, and the water quality of the Great Barrier Reef continues to decline as a result (Bartley et al. 2017) (see case study: Terrestrial chemical pollutants, particularly pesticides, entering the Great Barrier Reef lagoon). In south-eastern Queensland, the main Bremer River Catchment has been contaminated by discharges from sewage treatment plants, a coal mine, an abattoir and a power station, and conditions have not improved in the past 5 years.

Tasmania has seen gradual improvements in the condition of estuarine environments, with increased management significantly reducing metal loads and nutrient run-off (DEP 2020). Research on the contaminated Derwent Estuary has seen new and growing management and control of input waste, specifically from paper mills, wastewater treatment plants and aquaculture (Stevens et al. 2021). However, the state is still suffering from severely contaminated sediments from legacy human-activity practices, and these contaminants will persist for many decades.

In South Australia, major waterways in the Port River and Gulf St Vincent have ongoing water management issues, with impacts from nutrient-rich discharges and stormwater run-off. Seagrass has been lost due to poor water quality resulting from stormwater run-off and effluent disposal; however, significant improvements have been made to protect South Australian seagrass communities by limiting stormwater run-off entering the gulf. The state government is undertaking the largest seagrass restoration project in Australia to re-establish seagrass off the Adelaide coast.

Although there has been improved urban water management in Perth and Exmouth in Western Australia, surface run-off and dumping of waste from inland mineral extraction operations into urban areas still poses threats to the coastal ecosystems and public health.

Contaminant management

In the past 5 years, there have been several successes in innovative research and management practices to monitor and understand the effects of contaminants. Examples include the creation of a real-world ecotoxicological dataset of microbial community responses to urban wastewater (Ruprecht et al. 2020), the use of nuclear techniques to understand the effects from stormwater on aquatic organisms (Cresswell et al. 2017, McDonald et al. 2020), and updated water and sediment quality guidelines (ANZG 2018). Citizen science projects that engage with and educate the public and agricultural personnel have also increased to help monitor and reduce the use of contaminant-filled products (e.g. National Outfall Centre). Thresholds have also been developed for environmental quality indicators in water quality models (Sultana et al. 2020), with South Australia proposing a Blue Carbon Strategy for 2020–25 that will expand the production of detailed aquatic ecosystem condition reports. Since 2018, all states and territories have been making progress towards banning single-use plastics to help prevent plastics from entering waterways and oceans.

Over the past decade, Indigenous practices and sciences have been acknowledged and are gradually becoming integrated into decision-making and management practices. However, the impact of contaminants in waterways and coastal environments on communities, culture and environments across Country still needs to be recognised. Indigenous knowledge of coastal environments can be used to help understand the cultural and social impact of contaminants. There is also concern about the health impacts to coastal Indigenous communities from contaminants such as polybrominated diphenyl ethers (PBDEs) entering the marine environment and subsequently bioaccumulating in the food sources of many communities (Noziglia et al. 2018). The knowledge gained from the historical and spiritual connection between coastal Indigenous communities and their environment can help understand the disruptive impacts of pollution, and Indigenous practices for sustainable management can be integrated into the restoration of contaminated waterways (Ataria et al. 2019). It would be useful for Traditional Custodians if contaminants were mapped and a register established to warn about contaminated sites.

Case Study Terrestrial chemical pollutants, particularly pesticides, entering the Great Barrier Reef lagoon

Approximately 423,000 square kilometres of land drains to the Great Barrier Reef (GBR) lagoon, all of which can be a potential source of pollutants entering the lagoon. Uses of this land include cattle grazing (72% of the area); conservation (15%); other agriculture (5.8%); forestry (4.6%); mines, wastewater treatment plants, land-fills, and industrial and commercial sites (2.4%); and residences of 1.2 million people (0.3%) (ABS 2017, DES 2020). However, the composition of land uses is highly variable at different spatial scales.

Currently there are more than 40,000 industrial chemicals (Wang et al. 2020) and 9,500 pesticides (APVMA 2021) registered for use in Australia. Where these chemicals are used and disposed of, and their physicochemical properties (e.g. solubility in water) will determine where they end up in the environment (e.g. soil, sediment, water, biota). Kroon et al. (Kroon et al. 2020) recently identified antifouling paints, coal dust, metals, metalloids, marine debris, pharmaceuticals, personal care products and petroleum hydrocarbons as chemicals of emerging concern for GBR waters, but stated that the available monitoring data were insufficient to permit risk assessments. Consistent with this, Heffernan et al. (Heffernan et al. 2017) detected more than 5,000 organic chemicals in green turtle blood collected at 3 sites in the GBR lagoon. An extensive database of the annual amounts of suspended solids and nutrients and the concentration of approximately 60 pesticides entering the lagoon over 10 years has been generated. Other chemicals have been monitored on an ad hoc basis.

By 2015, 56 pesticides had been detected in GBR catchment and marine ecosystems (Smith et al. 2015), and 80% of samples collected between 2010–11 and 2014–15 contained mixtures of up to 20 pesticides (Warne et al. 2020b). Twenty-two pesticides were frequently detected in waters entering the lagoon (Warne et al. 2020a). By accounting for the concentration and temporal exposure of these 22 pesticides, it was estimated that less than 1% to 30% of aquatic organisms would experience harmful effects at the mouths of waterways entering the lagoon from 2015–16 to 2018–19. The greatest risk occurred in waterways of the Mackay–Whitsunday region (Warne et al. 2020a, Water Quality & Investigations 2020).

The pesticide risk condition on the 2019 Reef Water Quality Report Card for the GBR indicates that 97.2% of aquatic species across all GBR catchments were unlikely to experience harmful effects from pesticides (Queensland Government 2019). However, this represents the spatially averaged risk, and some regions and catchments are much more exposed than others. Inshore monitoring of 22 pesticides in 2018–19 revealed that 7 of 11 sites met the desired level of protection for the GBR (i.e. more than 99% of aquatic species) (Thai et al. 2020). In parts of the GBR lagoon not affected by flood plumes, the risk from these 22 pesticides is likely to be very low. However, current risk assessments only consider 22 pesticides and do not consider co-stressors, such as heatwaves, which can increase the risk posed to aquatic species (Negri et al. 2019), the lifelong exposure of organisms to very low pesticide concentrations and the toxicity of most breakdown products.

Mining and energy production

Many of the pressures on coasts from mining and energy production focus around the ports used for exporting mineral resources and on coastal infrastructure necessary to process offshore petroleum resources for export. The main pressures are pollution and changes to land use.

The National Pollution Inventory tracks facility-reported emissions of 93 substances released into the environment; 6 of the most common associated with mining and energy production are lead, copper, zinc, arsenic, cadmium and selenium (Figure 31). Although trends may be apparent for some substances (e.g. lead), in some cases most of the material reported comes from just a few facilities, and trends may depend on how estimates were made or whether facilities report each year. For example, almost all (98%) of the cadmium reported as released into water in coastal areas in 2018–19 was from the lead smelter at Port Pirie (South Australia) and the zinc refinery in the Derwent River (Tasmania), and a large increase in zinc released in 2012–13 was almost all due to a threefold increase reported by the Derwent River refinery.

Figure 31 Recent trends in metal emissions from coastal mining, minerals processing and energy operations

NPI = National Pollutant Inventory

Note: Data represent national emissions of 6 common metals released into water from energy production, mining, mineral processing and port facilities (NPI codes 0801-0809, 0911, 1701,1709, 2090, 2110, 2131-2133, 2139, 2611, 5212). Data were filtered to include only facilities located close to the coast (<2 kilometres from a coastline, inlet or coastal lake, as assessed on Google Earth).

Mining and minerals processing

Overall, the direct effects of mining on coastal areas are a weak pressure at the national scale. Other than sand and salt, few mineral resources are specifically associated with the coast. A handful of mines operate close to the coast, but most mining occurs further inland. Subtidal resources are rarely mined – nearshore manganese deposits have attracted some interest in the Northern Territory, but a moratorium on seabed mining there is likely to be made permanent. At least 3 more large salt field developments are currently being planned for north-western Australia.

Greater, indirect pressures stem from the transportation of ore to ports for international export and a limited amount of refining that occurs in Australia. These are also weak pressures at a national scale, although impacts can be important locally.

Although mining activities levelled off a few years ago and there have been fewer port developments or expansions in the past 5 years, there are some ongoing expansions of large ports in Western Australia and smaller port developments in other states like South Australia. However, increasing amounts of iron ore, coal and other mineral commodities are being exported, which likely means increasing losses of ore (dust from stockpiles, spillage while loading onto ships and so on). These losses can cause contamination in the local environment.

Such fugitive losses are largely unaccounted for, but impacts would be felt around port areas. Overall, the National Pollution Inventory shows no consistent trend in reported emissions of contaminants from coastal energy production, or mining and minerals processing (Figure 31).

In any case, Australia’s long history of mining (and poorer environmental regulation in the past) mean historical legacies may be more of a pressure than recent emissions. Although such pressures are well documented at some legacy sites, other information (particularly around ports) is contained in industry-commissioned reports and is not always easily accessible.

Gas plants

Pressures associated with energy production come from ports and facilities built for exporting liquified natural gas (LNG) across northern Australia (Western Australia, Queensland, Northern Territory). These pressures have levelled off since the construction of major plants ended and operation (exporting gas) commenced between 2015 and late 2018.

Industry monitoring during plant construction has generally found that impacts have been constrained within expected (and permitted) levels of disturbance; for example, losses of habitat associated with each development are restricted in size to less than tens of square kilometres. However, cumulatively, larger areas than necessary may have been lost because independent developments have been built for the same purpose. A more strategic planning approach could have minimised the total area disturbed.

Moreover, a net loss of coastal habitats such as seagrasses, coral reefs, mangroves and mudflats has probably occurred. Despite biodiversity offsetting programs becoming common in coastal developments in Australia, most offsets have been indirect, with little information about how and if compensatory programs ensure that an overall loss of habitat has been avoided.

Future LNG exports will continue via onshore (coastal) processing plants, and while some expansions of current plants might occur in the Northern Territory or Western Australia if new offshore fields are developed, further greenfield developments seem unlikely. Some offshore seismic exploration is still occurring, but planned exploratory drilling has not gone ahead in new areas such as the Great Australian Bight and now may be off the agenda permanently.

Although LNG export facilities have expanded in the past decade, diminishing supply has led to proposals for import terminals to supply the east coast domestic gas market; some new (port and regassification) infrastructure will be needed for this.

Nonetheless, future oil and gas developments are unlikely to extend impacts much outside the current footprint of existing ports and processing facilities; this footprint might even contract as infrastructure becomes redundant and is removed, and some areas are remediated. The decline of older Bass Strait and North West Shelf oil and gas fields means decisions about what to do with disused infrastructure will soon become important. Research is still needed to address whether to decommission and remove facilities completely, or whether there is ecological value in leaving some of the existing infrastructure in coastal areas.

Renewable energy

In terms of renewable energy, most solar farms are located away from the coast. Wind farms are all sited onshore in Australia, with many in Victoria, South Australia, Western Australia and Tasmania relatively close to the coast. Australia plans to more than double its capacity for wind generation in the next few years, although most of this new capacity will be located further inland; of 51 planned land-based farms (10.4 gigawatts), only 6 (0.6 gigawatts) will be within 2 kilometres of the coast, mainly in Tasmania. However, there are 14 offshore wind farm projects in the works for Australia (4C Offshore 2020, MUA 2020), with the most advanced proposal off the Gippsland coast in Victoria, so associated coastal infrastructure is likely to be an increasing pressure into the future.

Despite extensive wave resources identified along the southern coasts of Australia, ocean renewable energy is not yet commercially viable. A few full-scale wave devices have been tested at a proof-of-concept stage, but commercial arrays are unlikely for some time. Consequently, while the rapid development of renewable energy infrastructure will exert increasing pressures on the environment, little of this will be on coastal systems.

Artificial structures

Population growth and increasing development along the coast have resulted in the proliferation of artificial structures to support human activities (Bugnot et al. 2021, Floerl et al. 2021). These include vessel-related structures such as wharves, jetties, marinas and moorings; coastal defence structures such as seawalls, breakwaters and groynes; civil infrastructure such as bridge pylons; and structures introduced to support aquaculture or as artificial reefs.

Artificial structures affect the coastal environment through the direct replacement of natural habitats such as mangroves, seagrasses and sediments, as well as through a halo of impacts to areas surrounding the structure (Bugnot et al. 2021). They can change biotic interactions by altering food webs (Clynick et al. 2007), facilitate the establishment and spread of non-Indigenous species (Glasby & Connell 1999, Dafforn et al. 2012), and act as barriers to the movement of species between habitats (Bishop et al. 2017). Artificial structures can also modify coastal and estuarine habitats through the effects of ‘coastal squeeze’, in some instances exacerbating effects of erosion on a structure’s seaward side or at its flank. In addition to destroying habitat, some structures also degrade habitat; for example, wharves and piers built over seagrass can have an indirect impact due to shading (Shafer 1999). Where artificial structures modify the abundance of key species, they may also impact ecosystem functions such as fisheries production and maintenance of clean water (Mayer-Pinto et al. 2018).

In some areas of Australia, more than 50% of estuarine coastlines are modified by artificial structures such as seawalls (Bulleri et al. 2005, Dugan et al. 2011). Most modification tends to be associated with urban growth around major estuaries, such as Port Jackson (Sydney) and Port Phillip Bay (Melbourne), or with the development of large shipping hubs such as Port Botany (Sydney) or the Port of Port Headland (Western Australia). Recreational boating in Australia is supported by 356 marinas that occupy an area of 28.7 square kilometres around the coastline (Bugnot et al. 2021). In Australia, Sydney Harbour alone has almost 40 marinas that support around 35,000 vessels (Widmer et al. 2002).

The extent of artificial structures is projected to increase into the future, associated with continued growth of Australia’s coastal population, and the growing threat of inundation and erosion of coastal assets due to sea level rise. By 2029–30, Australian ports will handle an estimated 12.314 million 20-foot equivalent units of containerised freight and 3.217 billion tonnes of noncontainerised freight per year (BITRE 2010). This represents an increase of between 155% and 264% in freight, and 46.9% growth in the number of vessels supported by Australian ports since 2012–13. It is estimated that with the projected sea level rise of 1.1 m over the next century, up to $63 billion (replacement value) of existing residential buildings are potentially at risk of inundation (DCCEE 2011), necessitating either relocation, abandonment or, most likely, coastal defence.

The need for new artificial coastal defence structures can be reduced by using nature-based solutions instead (Airoldi et al. 2021), and by appropriately planning for the effects of sea level rise and storms. For example, oyster reefs are increasingly being established to not only bolster fisheries but also stabilise eroding estuarine shorelines. The recently developed national guidelines for nature-based coastal defence provide guidance on what approaches will be appropriate, and where (Morris et al. 2021).

The removal of structures that are no longer serving their original purpose, when accompanied by habitat rehabilitation works, can also reduce the footprint and impact of marine built structures. However, there are cases where it may be desirable to leave structures in place. For example, derelict oyster farms have in some instances provided the substrate for establishment of wild oyster reefs, which have considerable ecological value. Consequently, some state agencies are rethinking the management of derelict farms.

Where artificial structures are required, new structures can be designed, and existing structures modified, to maximise their ecological value (e.g. living seawalls; see case study: The Living Seawalls project in Sydney Harbour). Such ‘eco-engineering’ (Chapman & Underwood 2011, Browne & Chapman 2014) may include using eco-friendly materials in the construction of structures, and designing structures to maximise the amount and quality (e.g. complexity, light availability, wave exposure) of the habitats they provide (Glasby & Connell 1999).

Many more artificial structures will be built in the near future to protect our coastal assets from climate change, and increasing trade and vessel movements require the support of expanding vessel-related infrastructure. Additionally, aquaculture is a fast-growing sector and will contribute increasing numbers of artificial structures to our waterways. Management strategies for artificial structures might include:

  • minimising the footprint of artificial structures by developing multi-functional structures that serve dual purposes, and using nature-based solutions where possible (Dafforn et al. 2015)
  • applying marine spatial planning tools to avoid construction in sensitive habitats or habitats that are important larval/resource ‘sources’ (Bishop et al. 2017)
  • where built structures are required, designing these to also support ecological communities (eco-engineering) (Airoldi et al. 2021).

Case Study The Living Seawalls project in Sydney Harbour

Ecological (eco-) engineering in urbanised marine environments is a growing field with global significance (Chapman et al. 2018). The term describes how ecological understanding can be combined with engineering principles to mitigate the ecological impacts of artificial structures (Bergen et al. 2001). In Australia, efforts to ecologically engineer artificial structures have so far focused on intertidal seawalls and have been supported by more than 20 years of experimental research (Chapman et al. 2018). Three strategies have dominated:

  • using sloped or stepped (instead of vertical) designs to increase habitat availability
  • adding complexity that provides protection to inhabitants from predators and environmental stressors, and increases surface area for attachment (reviewed by Strain et al. (2018))
  • adding different types of habitat to provide a greater variety of environmental conditions for different species (reviewed by Chapman & Underwood (2011)).

Barangaroo Reserve is a recent example in Sydney Harbour where the first 2 strategies have been applied to the design of a new seawall as part of an urban renewal project. The project replaced a vertical concrete seawall, artificially aligned to suit commercial shipping and industrial purposes, with 1.4 kilometres of stepped sandstone blocks that followed the historical natural shoreline alignment of headland and coves. The sandstone was locally sourced from the adjacent escarpment, with the 9,315 sandstone blocks cut so they varied in size and shape. Use of heterogeneous blocks in a stepped design increased the intertidal area for marine species to colonise and created crevices where species such as oysters, snails, limpets and chitons could be protected from predators and environmental stressors. The stepped design also enabled people to access the marine environment and interact with its biodiversity. After block placement, natural weathering formed small rock pools that support filamentous green and brown as well as coralline algae.

The project was designed following government guidelines (Wiecek 2009) and with input from marine experts from the New South Wales Department of Planning, Industry and Environment and Kogarah Council. It also benefited from computer modelling that was used to individually design and cut blocks for the location.

There are also a growing number of examples in Sydney Harbour where the strategies listed above have been applied to increase the biodiversity of existing seawalls. Early studies drilled or excavated pits and crevices into seawalls (Chapman & Underwood 2011), enhancing rates of colonisation of species, though not necessarily of missing target species. Based on the learnings from this early eco-engineering, purpose-built water-retaining features were subsequently developed, which support species of algae, invertebrates and cryptic fish that would not otherwise be associated with seawalls (Browne & Chapman 2014, Morris et al. 2018). Advances in 3D design and printing have also provided new opportunities to incorporate more complex topographic features of natural habitats, such as rock pools, crevices and root structure, into seawalls. Small-scale pilot projects, using complex tiles fitted to seawalls, demonstrated the efficacy of topographic complexity in enhancing native species biodiversity (Ushiama et al. 2019, Strain et al. 2020), although the extent of benefits vary by location, the type of complexity provided and the scale of habitat modification (Strain et al. 2018). These pioneering studies have provided proof-of-concept for scaling up eco-engineering to entire seawalls.

The Living Seawalls project has developed a method of enhancing the topographic complexity of entire seawalls using concrete habitat modules. Modules are fabricated from moulds produced using the latest 3D printing technology and come in a range of designs that mimic habitat features such as rock pools, fish hollows, kelp holdfasts, sponge fingers and mangrove roots. Modules can be customised to locations and arranged in habitat mosaics, to maximise benefits to a wide range of species.

Mosaics of modules have been applied at scale to 9 seawalls in Sydney Harbour including Milsons Point, Sawmillers Reserve, Rushcutters Bay, Balmain East, Barangaroo, Fairlight and Clontarf. More than 900 habitat modules have now been installed since the first installation in October 2018.

Within hours of installation the modules are inhabited by microscopic life and invertebrates, and in just a few months, the modules are crowded with marine life. Colonisation of the modules by fish, invertebrates and algae is being monitored over several years to document how these installations benefit humans and marine life alike. Fundamental and applied research projects in this area are essential for the future management of artificial structures in the marine environment. The success of eco-engineering depends on multidisciplinary collaboration among ecologists, engineers, architects, developers, social scientists and other stakeholders, so that engineering, ecological and social goals may be simultaneously met.


Aquaculture can have negative effects on the environment, but the level and nature of effects depend on the type and size of operation, and the effectiveness of planning and management.

Global aquaculture production has been growing at around 5% per year over the past 2 decades (FAO 2020), and in Australia, aquaculture now accounts for approximately 38% of total seafood production by volume (Steven et al. 2019). In 2018, Australian mariculture produced 85,182 tonnes of seafood, most of which were finfish (73,270 tonnes) with smaller contributions from molluscs and crustaceans. Most of the value of Australian aquaculture production comes from high-value species such as pearls, salmonids, tuna and oysters, but over 40 species are currently commercially produced in Australia (DAWE 2020d).

Aquaculture around Australia

Current aquaculture efforts vary around Australia:

  • New South Wales has a significant oyster aquaculture industry, largely based on Sydney rock oysters.
  • Queensland’s biggest contributor to the aquaculture sector is prawns, although barramundi is also important.
  • South Australian aquaculture is heavily reliant on Pacific oyster production and aquaculture of southern bluefin tuna.
  • Tasmania has the greatest aquaculture production; salmonids are the most significant species produced, but there is also significant production of oysters, mussels and abalone.
  • Victorian aquaculture is mainly focused on abalone and salmonids (mainly rainbow trout).
  • Pearls are the most valuable aquaculture product produced in both Western Australia and the Northern Territory, although barramundi is also an important aquaculture species in the Northern Territory.

However, in all states and the Northern Territory, there are several new species under consideration for aquaculture. For example, there has been growing demand for seaweed products in Australia in recent years. While Australian seaweed aquaculture is in its early developmental stages, the AgriFutures Australian Seaweed Industry Blueprint (Kelly 2020) sets an aspirational target for a $1.5 billion domestic seaweed industry by 2040.

There is a long history of Indigenous aquaculture in Australia. Recent examples are limited, but include pearl oyster farming in the Northern Territory and a new cooperative research centre looking at tropical rock oyster aquaculture in northern Australia. But this is changing. The Darwin Aquaculture Centre is working on aquaculture projects with Indigenous communities, and the Indigenous Land and Sea Corporation is laying the foundations for a thriving and sustainable Indigenous aquaculture sector through its Indigenous agribusiness strategy.

Pressures from aquaculture

Aquaculture development is often controversial. Opponents suggest that farmed fish pollute coastal ecosystems with waste feed, faeces and chemicals that can adversely affect native plants and animals and ecosystem processes. Genetic pollution, escapees and reservoirs for disease are also often perceived as negatives of aquaculture. However, for shellfish at least, there is increasing evidence from Australia and internationally that selectively bred genotypes developed for aquaculture do not persist in the wild and do not hybridise with wild populations (Thompson et al. 2017).

Advocates say that aquaculture is among the most environmentally efficient food systems, that impacts are minor compared to other sources of protein production and can be managed, and that in some cases aquaculture may actually improve environmental outcomes. For example, seaweeds and shellfish can be cultured to mitigate nutrient inputs from other sources, by filtering nutrients from the surrounding water, reducing the potential for nutrient pollution (eutrophication) and the likelihood of algal blooms. Aquaculture infrastructure can also provide habitat to native species, and aquaculture can in some instances help support restoration efforts. For example, aquaculture can assist in the cultivation of species for the purposes of stocking, and reproductive oysters on farms provide a source of larvae for nearby oyster reef restoration projects.

The likelihood and potential severity of any environmental impacts will depend on various factors, such as:

  • type of species farmed
  • nature of the aquaculture operations (fed or not fed)
  • size and efficiency of farming operations
  • farming location (seabed type, depth, water movement)
  • prevailing conditions (weather, time of year)
  • surrounding ecology
  • interactive effect of other resource users (urbanisation, adjacent land uses and farming, fishing activities, tourism).

These factors should be taken into account when selecting sites for aquaculture development.

Increased nutrient loads from aquaculture, particularly fed-fish farming, can have significant impacts on the seabed and surrounding water quality (Black 2001), and if not managed effectively, can result in eutrophication (excess nutrients), which may cause harmful algal blooms. Aquaculture operations are usually highly regulated to address this risk. Impacts below or adjacent to fish pens are monitored to ensure compliance with environmental standards, and farmers seek to manage impacts by rotating fish within the pens and limiting feed inputs.

Although the impacts from fed aquaculture can be significant, they are usually limited to the area immediately around the pens. However, broader-scale impacts have been observed in systems where water exchange is limited (Ross et al. 2019).

Consequently, it is important to have good site selection protocols and a clear understanding of the hydrodynamics of the receiving waters before development is undertaken. As a result, modelling has become increasingly commonplace in aquaculture planning. All states and the Northern Territory have recently reviewed their aquaculture development strategies with a view to both identifying suitable areas for development and establishing sustainable practices (Tasmania, South Australia, Victoria, New South Wales, Queensland, Northern Territory, Western Australia).

Aquaculture research and management

The United Nations Food and Agriculture Organization has predicted that by 2021, more than half of the fish consumed globally will be produced by aquaculture, with global aquaculture production to reach 109.5 million tonnes by 2030 (FAO 2020). Achieving this level of production presents several significant challenges, and we have to acknowledge and understand those risks to be able to manage and mitigate them.

We need research to inform, support and improve spatial planning, and ensure that shared resource allocations are sustainable, and that ecosystem services are adequately represented and protected in the planning process. Biosecurity remains a high priority; obtaining a better understanding of the disease risks to and from aquaculture species, and the management of introduced species and disease transfer between aquaculture and wild populations, are key areas for research and development. Harmful algal blooms continue to threaten the viability of aquaculture operations in many areas, and research is still needed to improve prediction, monitoring and response mechanisms.

A relatively new risk that needs consideration is the role of land-derived nutrients, associated with aquaculture feeds, in marine processes. If aquaculture is to expand to the extent anticipated, we need to consider the potential impacts on hydrodynamics, local ecology and environmental flows. Similarly, given the increase in aquaculture activity in our coastal ecosystems, we need to better understand not just the individual impacts and interactions, but also the combined effects of multiple forms of aquaculture on environmental conditions.


Desalination is a process whereby treatment plants obtain freshwater from saltwater. Most desalination plants in Australia supplement the main water sources, providing water security to major cities in times of low rainfall or drought (see the Inland water and Urban chapters). They are usually located on the coast and draw in the seawater via an intake pipe, desalinate the water, then expel hypersaline (very salty) water back into the ocean via an outlet pipe.

The main potential ecological impacts of desalination arise from:

  • the footprint of the treatment plant on land
  • entrainment of seawater and marine organisms (e.g. plankton) into the intake pipe
  • the discharge of hypersaline brine and associated processing chemicals into the marine environment.

Large desalination plants operate in most major cities in Australia. In 2019–20, the Perth plant produced 140 gigalitres (GL), Melbourne 119 GL, Sydney 71 GL, Adelaide 40 GL and Brisbane 14 GL. The recent drought has meant that these volumes are substantially higher than for previous years, with the exception of Perth which has been relatively stable over the past 5 years. At times, Brisbane, Melbourne and Sydney plants have been on standby, entraining and discharging very little water.

While significant impacts of desalination have been quantified at other locations around the world (Roberts et al. 2010a), only limited effects have been observed at the operating plants in Australia. Entrainment of larvae is generally assumed to be limited considering the large volumes of seawater from which the intakes draw, and in situ videos provided by operators appear to show little influence of intakes on rocky reef fishes.

The discharge of hypersaline brine and processing additives appears to have little impact on sessile rocky invertebrates (Clark et al. 2018a) or fishes (Kelaher et al. 2019a). Generally, discharging into high-energy coastlines with high-velocity discharge jets forces the dense hypersaline water high into the water column, which then dilutes as it tumbles back towards the seafloor. A study of recruitment patterns near the Sydney desalination plant outfall found impacts to recruitment within 100 metres of the outfall, but these were likely due to changes in hydrodynamics rather than salinity or other forms of toxicity (Clark et al. 2018a).

Good hydrodynamic modelling and diffuser optimisation, along with appropriate ecotoxicological testing (Dupavillon & Gillanders 2009, Cambridge et al. 2019), have resulted in good practice with little observed effect on the marine or coastal environments. If desalination plants increase in their capacity, however, as is planned when dictated by water requirements, impacts may occur and should continue to be tested for at high running capacities.


Dredging aims to modify the shape of the seabed for shipping and infrastructure needs. It is often done to maintain safe shipping passage through the mouths of ports and harbours or along shipping channels, or during the construction of new maritime infrastructure, such as port construction or expansion. Dredging typically involves collecting sediments from the seafloor onto a barge or ship, then moving them to be dumped elsewhere, such as out to sea. The level of dredging activity in Australia has been relatively high since 2016, particularly in the north where there has been significant port development for the export of resources.

Although necessary for economic activity and maritime safety, dredging inflicts major environmental damage in the ‘dredging footprint’, or area that is dredged. Species inhabiting the dredged sediment are physically disturbed as they are removed, and the dumping of dredged spoils can smother or bury seabed habitats (see the Marine chapter).

Other impacts result from the resuspension of fine sediments, which impact biota beyond the dredging footprint. Resuspended sediment increases turbidity and increases light attenuation, hampering the ability of photosynthetic organisms to survive. This is particularly important in areas with key primary-producing habitat-forming species, such as coral reefs and seagrasses.

Resuspension of contaminated sediment can also release contaminants such as heavy metals into the water column where they are bioavailable to filter-feeding organisms such as sponges and lace corals (bryozoans) (Knott et al. 2009). In addition, resuspended sediments interfere with the delicate feeding appendages of some filter-feeding invertebrates, such a polychaete tubeworms. Silt curtains are used to contain the suspended sediments, but these are rarely completely effective and create extremely turbid conditions within the curtain.

Dredging in coastal waters is regulated by state government departments such as the Environment Protection Authority (EPA). Interestingly, there is low incidence of noncompliance to environmental standards, but this may be partly due to sampling design. Until recently, proponents of dredging have not been required to sample for impacts within the high- or moderate-impact zones, on the rationale that these areas are sacrificial. Overestimating the size of high-impact zones then pushes sampling further from the dredging footprint, which leads to low levels of impact detection. That is, operations are generally found to be environmentally compliant because monitoring occurs a long way from the impact. This has been addressed by the publication of EPA technical guidelines in Western Australia (known as EAG7), which prescribe sampling within the high-impact zone.

Another development is that spoils of capital dredging of more than 15,000 cubic metres cannot be disposed of within the Great Barrier Reef Marine Park, and must instead be taken ashore. However, maintenance dredging material can still be disposed of in spoil grounds. A recent expert panel found that the effects of dredged sediment on corals in the Great Barrier Reef was minimal, mostly due to the practice of avoiding dumping near corals (McCook et al. 2015).

Flow regimes

Flow regime has been described as the ‘master variable’ affecting environmental outcomes in rivers (Poff et al. 1997). The quantity, timing and frequency of flows in river systems affect all aspects of environmental systems and the human systems that rely on them (Arthington et al. 2018). Although much research has focused on the effect of flow regimes on inland river systems (see the Inland water chapter), flow regimes have important effects on the ecological functioning of coastal rivers, their estuaries and, in some cases, nearshore marine environments.

For example, Australian grayling (Prototroctes maraena) rely on flow pulses in autumn to stimulate spawning and transport eggs and larvae to estuarine environments (Koster et al. 2018), then flow pulses in spring to stimulate juveniles to migrate back into freshwater systems (Webb et al. 2018). Black bream (Acanthopagrus butcheri) breed at the interface of fresh and salt waters, and reducing freshwater flows shifts this interface further upstream where reduced habitat can affect breeding outcomes (Williams et al. 2012). Freshwater discharges from coastal rivers fuel nearshore productivity, from the Murray mouth (Bice et al. 2016) to the prawn fisheries of northern Australia (Broadley et al. 2020).

Flow regimes strongly influence water quality in coastal river systems by flushing the systems and replenishing them with fresh water. For example, environmental water released under the Murray–Darling Basin Plan from 2014 to 2019 led to the export of 1.27 million tonnes of salt from the Murray mouth – salt that would have otherwise degraded ecosystems of the Coorong and Lower Lakes (Bucater 2020). Freshwater flows that inundate lowland floodplains are also crucial for supporting food webs of rivers and their estuaries (Jardine et al. 2015).

Across Australia, flow regimes have been impacted by the regulation of rivers to support agriculture, industry (including mining), flood control and human consumption. Regulation can change both the total amount of water discharged from a river, and the timing and frequency of events within the overall flow regime. River regulation greatly reduces the occurrence of small (1–5-year interval) floods, disconnecting rivers from floodplains and starving them of organic matter inputs that can fuel downstream productivity.

The volume and timing of discharge is also being affected by climate change. For example, the recent long-term water resource assessment in Victoria found that a drying climate has reduced surface water availability by 21% across southern Victoria since 1975 (DELWP 2020).

The impacts of regulation on flow regimes of coastal rivers are unevenly distributed across Australia. Southern systems have lower natural inflows, but greater regulation, leading to greater impacts. Higher natural flows and less development in northern Australia means that flow regimes are only slightly impacted (Warfe et al. 2011, King et al. 2015).

Flow regimes are being partially restored through environmental flows – water released specifically for environmental purposes. The Murray–Darling Basin Plain aims to restore 20% of water being used for irrigation to the rivers of the Basin, although this is only 8% of mean annual flows. Many coastal rivers outside the Basin also have environmental flows programs. Active management of these environmental water entitlements (targeting water releases to specific environmental processes and outcomes; (Horne et al. 2017)) means that the limited volumes of environmental water available are being used efficiently to maximise environmental return.

Freshwater flows in much of Australia are permanently altered and will not ever return to anything approximating an undisturbed state. However, management actions – particularly over the past decade – have improved river flows, with demonstrable benefits for environmental conditions. Further improvement in flow regimes will depend on programs that progressively increase efficiency in agriculture (thus reducing the amount of water consumed), and public support for continued and expanded restoration of flow regimes. However, the benefits of such improvements will be at least partially offset by the continuing effects of climate change.