Estuaries

Estuaries are where rivers meet the sea. They are the lower reaches of rivers that undergo substantial salinity change due to the mixing of freshwater with seawater. They may be permanently or periodically open to the sea with salinities that vary from almost fresh to very saline. Environmental condition may be stable over long periods of time or change frequently or rapidly. Estuaries are, therefore, complex and highly variable environments that often appear to be unpredictable.

Since estuaries are at the bottom end of catchments, they are subject to all the impacts on the catchment. As many catchments in Victoria are degraded, most estuaries could be considered to be potentially at risk. Few would be considered to be in a natural or near natural condition.

So what is a healthy estuary? To try and answer this question, EPA Victoria has been undertaking a study of estuary water quality and biology for several years. The major aims of the study are to determine appropriate estuary indicators for assessing environmental condition and for identifying threats, and to develop preliminary environmental quality guidelines and targets.

Victoria's three largest embayments (Port Phillip Bay, Western Port and Gippsland Lakes) can also be thought of as estuaries. EPA monitors these embayments as part of our fixed site monitoring program. EPA, with a range of partners from the local to national level, including Melbourne Water and Department of Environment and Heritage (DEH), is centrally involved in the development of water quality improvement plans for these large embayments.

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