Fish kills

If you want to report a fish kill, please ring the Fishers Watch hotline on 1800 043 536 or refer to the fish kill investigating and reporting protocol for more details.

Water quality can have a range of impacts on fish. The impacts can be acute, resulting in fish kills, or chronic, impacting on breeding, growth and development.

A fish kill is defined as "any sudden and unexpected mass mortality of wild or cultured fish".

Fish kills are often very visible events, which cause considerable interest and concern to the public and the media because they're often perceived to be the result of pollution or contamination of waters. In fact, there are many and varied causes of fish kills, and a large proportion are due to natural events.

Fish kill. Photo: Allan Lugg

The range of causes of fish kills in NSW is shown below. In just under half the fish kill events, the cause is not known. Where it is known the majority of cases are caused by one of three most common causes:

  • low dissolved oxygen
  • pesticide / chemical pollution
  • sewerage discharge or other pollution.

Causes of fish kills in NSW. NSW DPI.

Note: DO = dissolved oxygen. ASS = acid sulphate soils discharge