Threats to estuaries

The health of our estuaries is threatened by coastal development, declining water quality and loss of habitat for native species.

Estuaries are impacted by pressures from human activities as well as natural events such as storms and floods. They are complex, dynamic and relatively fragile environments. Estuaries are particularly sensitive to inappropriate catchment development, increased levels of sediment and nutrients and the degree of tidal flushing – the exchange of fresh water and ocean water.

Common threats to estuaries

Aerial view of Newcastle Harbour and Lower Hunter

The health of estuary ecosystems is threatened by:

  • increased nutrients and algal blooms
  • loss of habitat and biodiversity
  • contaminants and pollutants
  • accelerated rates of sedimentation
  • disturbance of acid sulfate soils
  • changes to freshwater and tidal flows
  • invasive species
  • climate change.

What we do about threats to estuaries

Monitoring and reporting

We work to manage and protect estuaries. Our scientists conduct research and monitor the health of estuaries. We regularly collect and analyse data on the physical properties of estuaries, including their habitats, biodiversity and water quality.

Identifying risk and threats

We use past surveys to compare with present estuary conditions and we work to identify the major threats to estuaries and the causes of these threats.

To help with monitoring, evaluating and reporting on estuary health, we have developed the Coastal Eutrophication Risk Assessment Tool or CERAT. This tool allows us to identify current threats and probable outcomes and is used to inform land-use planning by local councils.

Causes of threats to estuaries

Population growth and coastal development are two of the key causes of threats to our estuaries.

  • Population growth

Over 80% of the population of New South Wales lives in coastal areas, including the shores of estuaries. Much of the northern and central coastline of NSW is far more densely populated and developed than other parts of Australia and is under greater environmental pressure.

Coastal areas attract millions of visitors in summer holidays and estuaries are often the focus of outdoor activities such as recreational fishing and boating, placing additional strain on natural resources and infrastructure.

  • Urban coastal development

Urban development has had a negative impact on estuarine environments. Channels have been dredged, wetlands drained, saltmarshes and tidal flats filled, waters polluted, and shorelines reclaimed to accommodate housing, transportation, and agriculture needs.

Overuse of resources and unchecked land use practices have resulted in unsafe water for swimming, oyster harvesting closures, harmful algal blooms, unproductive fisheries, loss of habitat, fish kills, and risk to human health.

Major issues affecting estuaries

Estuary management committees, councils, agencies and the community have identified several issues affecting estuaries including:

  • declining estuarine water and sediment quality
  • degradation and loss of estuarine habitats
  • unsustainable coastal development and use of estuarine resources

Declining water quality and sedimentation are regarded as one of the most serious issues affecting NSW estuaries. Elevated nutrients and sedimentation are largely the result of inappropriate catchment land use practices, land erosion, sewage discharge and urban run-off.

  • Sediments and nutrients

    Sediments infill estuaries and can smother marine life. Excessive nutrients cause eutrophication and excessive growth of algae. Algal blooms are becoming common in many estuaries. Eutrophication poses a serious threat to estuarine ecosystems.

  • Heavy Metals

    Pollution from mercury, lead, copper and other heavy metal is a localised problem. Heavy metal hot spots include Lake Macquarie, Sydney Harbour and the Hunter River. Controls on industrial discharges and the use of antifouling paints have reduced heavy metal levels in many areas. Problems remain in areas requiring maintenance dredging or where sediments may be disturbed and resuspended into the water column.

  • Litter

    Urban estuarine areas are most affected by litter. Litter reduces the scenic and recreational values of an area and degrades habitats where it accumulates in areas such as mangroves and wetlands.

Many of the environmental issues that relate to water quality and habitat loss overlap:

  • Degradation of coastal lakes and lagoons

    Estuarine environments throughout much of NSW are declining because of eutrophication and sedimentation, acid sulfate soils runoff, coastal development, loss of habitat and overfishing. Intermittently closed and open lakes and lagoons (ICOLLs), which have restricted exchange of ocean water and tidal flushing, have been particularly affected by catchment runoff.

  • Decline in seagrass

    Seagrass beds are very important ecosystems. Elevated nutrients and sediments have caused serious dieback of temperate seagrass beds in many estuaries. Around half of the seagrass beds in the estuaries of NSW have been lost. The remaining seagrass beds are under threat from inappropriate coastal development and habitat degradation.

  • Loss of mangroves and saltmarshes

    Significant losses of saltmarshes and mangroves have occurred near urban areas through reclamations, drainage and other developments. This affects fish and other marine life, which are dependent on these areas as nursery and feeding grounds.

  • Loss of coastal wetlands

    Significant losses of coastal wetlands have occurred as a result of agricultural drainage, flood mitigation works and other developments. These activities often disturbed acid sulfate soils. Up to 60% of coastal wetlands have been lost or are showing evidence of serious degradation.

Rapid population growth and expanding development is affecting estuarine ecosystems. Urban, industrial and port development, tourism, and other uses have been responsible for significant degradation of the coastal strip of NSW.

Threats from coastal development include:

  • Fishing

    Over-harvesting of fish by commercial and recreational fishers and inappropriate aquaculture practices such as trawling, have resulted in a decline in fish stock, juvenile fish and threaten estuarine food webs.

  • Acid sulphate soils

    Acid sulfate soils are natural sediments that contain iron sulfides. They are common along the NSW coast. When disturbed or exposed to air these soils can release acid, damaging crops, waterways, built structures as well as harming animals and plants.

  • Tourism

    Tourist facilities, infrastructure and accommodation are usually located as close to coastal attractions as possible. This may affect the natural environment, quality of life and scenic amenity of an area with loss of habitats, declines in fisheries and deteriorating water quality.

  • Sewage

    Sewage and stormwater runoff are major sources of nutrients associated with urban areas. Most effluent discharged in NSW is tertiary treated but many areas remain unsewered. Problems have been experienced by the oyster industry as a result of human intestinal viruses being present in estuarine waters.

  • Draining of coastal wetlands

    Significant losses of saltmarshes and mangroves have occurred near urban areas through drainage and reclamation. Perhaps more significant is the loss of coastal wetlands as a result of agricultural drainage works on coastal floodplains. These losses have affected fish and birds that use these habitats. Drainage may lead to issues associated with acid sulfate soils.

The widespread degradation of intermittently closed and open lakes and lagoons (ICOLLs) is a serious local and national problem. Major causes are elevated nutrients, sedimentation, pollution, inappropriate coastal development, flood mitigation and overfishing. Of particular concern are the unique coastal lakes that are not represented in the less populated and less degraded parts of Australia.