Fish kill events

A fish kill event involves the death of a large number of fish or other aquatic animals (such as crabs or prawns) over a short period of time and often within a defined area.
Last updated: 15 September 2023

What causes fish kill events?

Fish kill events can occur due to a wide range of factors including:

Cause Details
Natural deaths of adults This may occur after spawning.
Migrating fish being trapped in areas of poor water quality This can occur naturally or because of artificial structures in waterways that act as barriers and prevent escape.
Disease Disease can be due to natural and introduced parasites, bacteria, fungi or viruses. Poor water quality can cause stress which increases animals susceptibility to diseases.
Low dissolved oxygen One of the most common causes of fish kills. It can occur due to poor mixing resulting in anoxic conditions; rapid mixing following flow events or other occurrences which disturb deeper anoxic waters and sediments; consumption of oxygen by phytoplankton, bacterial blooms following the decay of an algal bloom,  input/mobilisation of large amounts of organic matter, or coral spawning.
Sudden change in water quality A rapid change in salinity, pH, turbidity, dissolved solids or temperature can stress fish even if conditions remain within normal tolerances.
Contaminants in our waterways  Common contaminants linked to fish kills include hydrogen sulphide, nutrients (such as ammonia), metals, hydrocarbons and pesticides. Contaminants can reach levels of concern after ‘first flush’ flow events (where accumulated materials in the catchment are flushed into an aquatic system over a short period), pollution events (e.g. chemical spills) or when they are released from sediments following disturbance.
Physical irritants These include suspended sediment, algal cells and bacteria that interfere with respiration (i.e. block fish gills)
Algal toxins These are produced by some phytoplankton species under certain conditions.

Read more in our infographic about fish kills and the connection with algal blooms.

Reporting a fish kill

The Department of Water and Environmental Regulation and Department of Primary Industry and Regional Development (DPIRD Fisheries) jointly manage the state's Fish Kill Response, supported by other state and local government agencies.

We need members of the public to report incidents as quickly as possible so that we can respond.

If you see a fish kill, please report it immediately to:

For your safety please do not touch dead or dying fish, and avoid contact with the water in the area until our officers can assess the risk. This includes not using fish in the area of a fish kill event as bait; in case there is risk of transferring disease or contaminants.