What is an Estuary?
An estuary is a partially enclosed body of water where fresh water and salt water meet. As the Georges River flows down into Botany Bay its waters form part of an estuary, including the bays around Kogarah and Oatley.
Estuaries are vital ecosystems and form the basis of the coastal food chain. They provide a rich diversity of habitats for aquatic and terrestrial animals. Estuaries are known as "the nurseries of the sea," as they form breeding and nursery grounds for many fish and shellfish, including around 70% of fish species important for the commercial fishing industry.
Important components of the estuary around the Georges River region include seagrasses, wetlands, mudflats and mangroves. Community members and visitors enjoy the recreational benefits of healthy estuaries such as boating, fishing, swimming and bird watching.
Through new strategic policies and plans, the Georges River Council and local stakeholders have developed an estuary management plan to protect these natural assets.
What are Wetlands?
Wetlands are a critical part of our natural environment. They protect our shores from wave action, reduce the impacts of floods, absorb pollutants and improve water quality. They provide a habitat for animals and plants and many contain a wide diversity of life, supporting plants and animals that are found nowhere else.
The Georges River Region has many diverse wetland areas, with some small in size while others are relatively large, covering thousands of square metres each.
Shipwrights Bay wetland is the most recently created wetland. It collects and treats stormwater from the end of Coogarah St in Blakehurst.
What is Sediment?
When the ground is left bare by human activities including clearing, construction and vehicle use, the soil is easily washed away when it rains. When soil, sand, dust, cement, paint and building debris reach the waterways, they can:
- Block drains
- Increase the risk of flooding
- Spread weeds to bushland
- Result in algal blooms
- Cause health problems for swimmers
- Smother and suffocate water plants and animals and impact on their ability to reproduce.
One of the strategies used by Council to stop sediment entering the river from the stormwater system is the installation of litter traps.
Other strategies to reduce sediment in the Georges River and surrounds include:
- Protecting aquatic habitats from pollution
- Controlling development practices
- Managing bushland and weeds.
What are Mudflats?
Mudflats are coastal wetlands that form when mud is deposited by tides or rivers. They are found in sheltered areas such as bays, bayous, lagoons and estuaries.
Expanses of mudflats are found in the bays around Georges River. They are exposed at low tide and covered by shallows as the tide moves in and out twice a day, bringing nutrients to the many organisms living there.
Mudflats form vital intertidal areas which provide habitats and feeding grounds for a variety of plants and animals. Migratory birds from Japan, China and Russia often rest and feed in these areas to build up strength before their long flight home.
Next time you're near some mudflats watch out for wading birds feeding on molluscs, worms and small crustaceans that live in the mud.
What are Seagrasses?
Seagrasses are aquatic flowering plants that form meadows in shallow, clear water. They are sometimes known as the lungs of the sea, as one square kilometre of seagrass can generate up to 10 litres of oxygen a day.
Healthy beds of seagrass often indicate good water quality and estuary health. In recent times, seagrass has reportedly been increasing in the Georges River estuarine area.
Seagrasses provide feeding grounds for wading birds, turtles, herbivorous fish, molluscs, and sea urchins. Many other aquatic species feed on seagrass throughout their life cycles.They act as a nursery for juvenile fish, crabs and prawns. Fish such as mullet, tailor, bream and flathead rely on seagrass beds for protection. Seagrass also helps improve water quality by:
- Trapping and stabilising sediment
- Preventing bank erosion
- Filtering water to remove sediment and nutrients.
What are Mangroves?
Mangroves grow along sheltered shorelines and play a vital role along the Georges River, including:
- Trapping silt and pollutants
- Stabilising shorelines
- Supplying nutrients to the food chain
- Providing shelter for many animals.
While NSW has five species of mangrove, it is the grey mangrove Avicennia marina that is found around the Georges River. This mangrove has adapted to the salty conditions by taking up water through its roots and excreting excess salt through its leaves. This mangrove also has "breathing roots" (pneumatophores) which stick out above the mud to absorb oxygen from the air.
The floor of a mangrove forest provides habitat for a huge number of crabs, oysters, barnacles, limpets, marine snails, worms, prawns and fish. Fruit bats feed on mangrove flowers and birds roost in the mangrove branches.
Mangroves help in many ways to clean our estuary. They filter run-off, trap sediment and allow it to settle and remove heavy metals, nitrogen and phosphorous.