Fish kills

Identified fish kills in 2019 due to environmental conditions

Location and date kill observed

Cause and extent

Murray Darling Catchments

Darling River, Menindee (6 Jan)

Affecting approximately 45 km of the Darling River below the Menindee Main Weir including Menindee township

  • Suspected to be caused by low dissolved oxygen levels triggered by a sudden drop in temperature that disrupted an existing algal bloom with mixing of hypoxic water through the water column
  • Hundreds of thousands of fish affected of a range of species

Lake Keepit (Namoi River) (11 Jan)

  • Low dissolved oxygen as lake level dropped and hot weather
  • Small numbers of Golden Perch (<10)

Lake Burrendong (Macquarie River) foreshore (12 Jan)

  • Recent localised storm activity that produced a flow event that contributed organic debris into the lake resulting in a sudden reduction in dissolved oxygen levels when the organic debris started to decompose
  • Over one thousand fish observed namely Carp and Redfin Perch with small numbers of native fish
Lower Murrumbidgee from Hay to Balranald (Late Dec and 9 Jan)
  • Water quality in all weir pools is deteriorating with low dissolved oxygen levels
  • Small numbers of dead fish (<10) observed in Redbank Weir before Christmas and in the Balranald Weir Pool on 9 Jan
Coastal Catchments

Lake Cathie / Innes near Port Macquarie (8 Jan)

  • Deaths suspected to be caused by low levels of dissolved oxygen from high water temperatures and low lake water levels with no flushing
  • Hundreds of fish reported including Bream, Tarwhine and Whiting

Note: Fish kills of <100 fish were reported at Jimmy’s Beach (Karuah River) on 13 Jan and at Bowna boat ramp (Lake Hume) on 15 Jan which related to fishing activities and were not caused by environmental conditions.


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.

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

A chart showing the various causes of fish kills