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Fish kills

A fish kill is defined as a significant and sudden mortality of wild or cultured finfish and other species such as prawns and crabs. Such events are generally characterised by large numbers of aquatic animals dying over a short period of time, usually in a clearly defined area.

These may be caused naturally: for example, unseasonal weather producing rapid changes in temperature may result in fish kills since many species lack the means of body temperature regulation. Human (anthropogenic) activities that adversely affect the health of waterways, such as the discharge or spillage of potentially toxic chemicals may also cause fish kills.

Anthropogenic impacts also include the degradation of waterways causing interference to the natural flow and poor land use practises that result in the build up of excessive nutrients and subsequent excessive growth of aquatic plants and algae. At night (when photosynthesis ceases), respiration by these plants can deplete the dissolved oxygen concentration sufficiently to result in fish mortality.

Since 2000, between 15 and 35 fish kills have been reported in WA each year, with 70% of these occurring in major waterways of the State's south-west. It is important to try to determine the cause of any fish kill in order to prevent future occurrences by understanding and improving the environmental factors that cause poor water quality. A rapid response is therefore necessary to collect information regarding the species of fish killed, water quality variables and other environmental conditions.

In Western Australia, the Department of Fisheries is responsible for the management of fish kill incident response with considerable support from the Department of Water. Under this arrangement, each department takes a role in responding to fish kill incidents depending on the type of aquatic environment and the location of the water body as follows:

  • The Department of Fisheries is the lead agency for Fish Kill Incident Response and coordinates the response to incidents occurring in the marine environment. The Department of Fisheries also takes the lead role in coordinating the response to a fish kill incident in any aquatic environment if the incident is caused by disease, fishing activity or introduced aquatic organisms.
  • The Department of Water coordinates the response for inland, riverine and estuarine waters and investigates as appropriate. If it appears likely that the event is caused by pollution, the incident will then be referred to Department of Environment and Conservation.
  • When an incident occurs at a location where the coordinating agency does not have sufficient resources (officers and equipment) to respond, assistance is sought from the other agency.

If you see a fish kill, please report it immediately to the nearest Department of Water or Department of Fisheries office. Contact details for these as well as an instructional brochure can be found at

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