Estuarine ecosystems are highly complex and dynamic environments. Since estuaries are at the bottom end of catchments, their condition can be affected by activities occurring within the upstream freshwater catchment. Where the condition of catchments, rivers or estuaries is poor, there are likely to be additional impacts on the marine receiving waters and coastal areas.
The majority of Victoria’s estuaries are brackish mouths of rivers and streams that flow directly into the ocean or into large marine bays (such as Port Phillip Bay, Western Port and Corner Inlet). There are more than 100 estuaries in Victoria, 83 of which exceed one kilometre in length. The definition of estuaries also includes coastal barrier lagoons (such as the Gippsland Lakes) and some coastal inlets (such as Anderson Inlet).
Many of Victoria’s estuaries close intermittently as a result of sand bar formation at the estuary entrance. This usually occurs during periods of low freshwater inflow. Intermittently closed estuary entrances are a natural feature of the Victorian coastline and can be critical to the ecology and physical form of estuaries.
It is vital to understand the links between the values of estuaries, threats to those values and how management activities can reduce threats and improve environmental condition of estuaries. A consistent method for assessing the environmental condition of Victorian estuaries has been developed: the Victorian Index of Estuary Condition (IEC). The IEC assesses estuarine resource condition for the purposes of:
- Reporting on the condition of estuaries across Victoria;
- Assisting the prioritisation of management investment among estuaries; and
- Providing a baseline for assessing long-term changes in resource condition.
The IEC consists of five themes: physical form, hydrology, water quality, flora and fauna. Victorian estuaries will be monitored in 2017-2020 to deliver the first state-wide IEC assessment