Estuaries are the places where rivers and the sea meet. They are typically semi-enclosed coastal bodies of water with a connection with the open sea and within which seawater is measurably diluted with fresh water from land drainage. There are 40 estuaries within the Corangamite region, of all shapes and sizes. Estuaries of the Corangamite region are highly valued for recreational use, particularly the Barwon River estuary and the numerous estuaries along the Great Ocean Road.

The region’s estuaries are also important environmental assets of the region’s coastline. They support a range of distinctive aquatic and terrestrial plants and animals, including rare and threatened species and communities. They are important drought refuges, provide significant breeding and feeding areas for birds, and spawning areas and nursery habitat for fish. Vegetation and saltwater marshes (including the nationally vulnerable Coastal Saltmarsh) adjacent to estuaries maintain water quality, assist with nutrient cycling, and provide a buffer to catchment-derived sediments and pollutants entering the marine environment.

The Barwon River estuary is the only estuary in the region that is permanently open. All the rest are classed as “intermittently open/closed estuaries”, which means they sometimes close to the ocean.  Corangamite CMA regulates artificial openings of estuaries throughout the region. An artificial opening most commonly occurs when the estuary mouth is closed off from the ocean due to a berm (a sandbar) that has naturally built up, meaning the river water cannot empty into the ocean. The region’s estuaries are normally quite resilient to coastal processes such as tidal exchanges, shoreline recession and natural estuary openings.

Habitats in estuaries include shallow wetlands, saltmarshes, mangroves, seagrass beds, sandy and muddy sediments as well as the water column itself. These habitats support a range of waterbirds, fish and invertebrates. The survival, health and distribution of these plants and animals are dependent on various physical and chemical processes operating in each estuary.

Anglesea River estuary