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Estuarine ecosystems are highly complex and dynamic environments

Since estuaries are at the bottom of catchments, activities occurring within the upstream freshwater catchment can affect their condition.

Where the condition of catchments, rivers or estuaries is poor, there are likely to be additional impacts on:

  • marine receiving waters
  • coastal areas.

Estuaries located in Victoria

There are more than 100 estuaries in Victoria. Most of Victoria’s estuaries are brackish mouths of rivers and streams that flow directly into:

  • the ocean
  • large marine bays, such as Port Phillip Bay, Western Port and Corner Inlet.

The definition of estuaries also includes coastal barrier lagoons such as the Gippsland Lakes and some coastal inlets such as Anderson Inlet.

Closed estuaries

Many of Victoria’s estuaries close intermittently because of:

  • sand bar formation at the estuary entrance
  • low freshwater inflow.

Intermittently closed estuary entrances are a natural feature of the coastline and can be critical to:

  • the ecology of estuaries
  • the physical form of estuaries.

Policy and guidance for estuaries

The policy for managing Victoria's rivers, estuaries and wetlands is set out in the Victorian Waterway Management Strategy.

Assessment of Victoria’s estuaries using the Index of Estuary Condition

The Index of Estuary Condition

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 the environmental condition of estuaries. A consistent method for assessing Victorian estuaries' environmental condition has been developed: the Index of Estuary Condition (IEC).

The Index of Estuary Condition (IEC) is a method for assessing the environmental conditions of our estuaries for the purposes of reporting on the condition of estuaries. It also:

  • assists with the prioritisation of management investment among estuaries
  • provides a baseline for assessing long-term changes in estuary environmental condition.

Index of Estuary Condition: results 2021

The IEC results from 2021 gives a snapshot of the environmental condition of 101 large estuaries.

Improving our knowledge of estuary environmental condition and threats can guide the way we manage these ecosystems. This will benefit communities and the environment.

The IEC took over a decade to test and refine. This work means that assessments will be consistent and rigorous. Similar condition indices are also used for Victoria’s rivers and wetlands: the Index of Stream Condition and Index of Wetland Condition, respectively.

The IEC measures 5 important aspects of environmental condition:

  • hydrology
  • physical form
  • water quality
  • flora
  • fish.

Key findings of the 2021 report

Excellent estuaries

  • 13% of Victoria’s estuaries were in excellent condition.
  • These estuaries are located along the Gippsland coastline, downstream of forested landscapes.

Good estuaries

  • 25% of Victoria’s estuaries were in good condition.
  • You can find these estuaries spread along the coastline, downstream from landscapes without intensive land use.

Moderate estuaries

  • 32% of Victoria’s estuaries had moderate conditions.

Poor estuaries

  • 25% of estuaries were in poor condition.
  • 5% were very poor.

Estuaries rated as either poor or very poor were in catchments with either intensive:

  • agriculture
  • urbanisation.

Assessing waterways in the future

Statewide condition assessments will be rotated among estuaries, wetlands, and rivers, with each waterway type assessed approximately every decade.

This monitoring frequency reflects that changes to the environmental condition of waterways are likely to be slow at broad spatial scales.

However, there may be more rapid changes in response to new threats or management interventions at individual estuaries.

Periods between IEC assessments

In the periods between IEC assessments, management decisions may be refined with updated information from targeted monitoring of key aquatic values and threats in specific estuaries.

This does not mean there may not be rapid changes to new threats or waterway management at individual estuaries.

We are grateful for all contributors to the development of IEC, which included representatives from:


Index of Estuary condition data is available via DataShare, a search discovery tool that enables assessment of DEECA's spatial data resources.

Page last updated: 08/09/23