Climate change impacts on our estuaries

• Estuaries are coastal waterways where rivers and streams meet the ocean. They support diverse and unique ecosystems including seagrass, soft sediments, mangroves and saltmarsh, and marine animals from shellfish to dolphins.
• Healthy estuaries support tourism, recreation, shipping, aquaculture and fishing, and are extremely important to the NSW economy and way of life.  
• Estuaries are being affected by climate change. Waters are warming and acidifying, and sea-level rise is causing higher, more extensive and more frequent inundation of estuaries and nearby low-lying areas.
• Development adjacent to estuaries is vulnerable to sea-level rise.
• Improving our understanding of how estuaries will change in response to threats such as sea-level rise will improve future mitigation and adaptation strategies. 

An estuary is a partially enclosed, coastal water body where freshwater from rivers and streams mixes with saltwater from the ocean. The water is brackish (saltier than freshwater, but not as salty as sea water). Because estuaries lie at the interface between riverine and marine environments, they are influenced by both freshwater inflows and tidal exchange. 

NSW’s 184 estuaries are important to NSW residents because they: 

• are home to most of our population; around 85% of NSW’s people live within 50 km from the coast
• support fishing; commercial and recreational fishing around NSW estuaries is worth nearly $600 million each year
• sustain shipping and tourism, such as Sydney Harbour
• support recreation; activities such as boating, fishing, swimming, diving, windsurfing and bird watching are common in estuaries
• hold cultural values; many NSW estuaries are significant to First Nations people. 

Estuaries are also a vital component of our environment. 

Estuaries are highly productive ecosystems and are rich in biodiversity. A large number of birds, mammals, fish and other wildlife live in and around estuaries. Many freshwater and marine organisms depend on estuaries as part of their reproductive cycles, and migratory birds often make estuaries a stopover. 

The wetland plants that live in and around estuaries protect and stabilise the shoreline from erosion, and help filter pollutants from the water. This includes sediments, nutrients, plastics, pesticides, herbicides and heavy metals. This function also makes them susceptible to degradation due to impacts of the trapped pollution. 

NSW estuaries may be named and characterised as: 

• drowned river valleys (for example, Hawkesbury River, Georges River and Port Hacking)
• barrier rivers (for example, Tweed River, Richmond River and Shoalhaven River)
• creeks (for example, Jerusalem Creek, Tallow Creek and Wowly Gully)
• lakes (for example, Wallis Lake, Tuggerah Lake and Lake Illawarra)
• lagoons (for example, Belongil Creek, Deep Creek and Woolgoolga Lake)
• back-dune lagoons (for example, Swan Lake, Nadgee Lake and Goolawah Lagoon)
• bays (for example, Jervis Bay, Botany Bay and Batemans Bay). 

Many of these estuaries are naturally intermittently open to the ocean. Some are naturally open or depend on human intervention to maintain open entrances. 

Climate changes to the ocean and catchment affect estuaries. Climate change was recognised as a major threat to estuaries in the NSW Marine Estate Threat and Risk Assessment. 

Estuaries are particularly vulnerable to the impacts of climate change because: 

• as the links between rivers and the ocean, estuaries are affected by changes in the catchment (temperature and rainfall changes) and by ocean changes (temperature, chemical and sea-level changes)
• they are more sensitive to the impacts of acidification; temperature rise and rainfall changes
• the land near many estuaries is low-lying, so nearby development and infrastructure is more threatened by sea-level rise than the open coast. 

Climate change is having significant effects on NSW estuaries: 

• Estuarine waters in NSW are rapidly warming and acidifying.
• Sea-level rise is causing more extensive and more frequent inundation of estuaries and nearby low-lying areas. In some estuarine areas, the number of days with some inundation of low-lying streets has more than doubled over the last few decades. Currently, around 3,345 buildings are exposed to estuarine inundation at a 1 day per year (exceedance) frequency. By 2100, under the same inundation frequency, exposure is projected to increase to between 50,700 and 86,700 buildings under low (SSP1-2.6) and high (SSP3-7.0) emission scenarios, respectively.
• More frequent and severe weather events will cause storm surges, exacerbating the impacts of sea-level rise.
• Sea-level rise is also increasing the tidal penetration of open estuaries and changing when intermittently open lagoons are linked to the ocean.
• Lagoons and wave-dominated river estuaries are warming and acidifying much faster than originally predicted. 

Such changes can have social and economic consequences. In NSW, 4 out of 5 people are likely to have significantly altered lifestyles as estuaries are affected by climate change. 

To help estuary managers consider climate change in their work, adaptation guidance is available on the climate-adapted estuary management page. 

The NSW Government is taking action on climate change through multiple pathways, including the Climate Change (Net Zero Future) Act 2023, the NSW Climate Change Adaptation Strategy and the NSW Climate Change Adaptation Action Plan 2025–2029. 

Sea-level rise and coastal hazards - NSW Government

Coastal hazards under sea-level rise: Estuarine inundation snapshot - NSW Government 

Climate change in NSW estuaries - University of New South Wales

CoastAdapt

Rising tides: Tidal inundation in south-east Australian estuaries - Academic paper