Millions of Fish Dead in Australia River Following Low Oxygen Levels, High Temperatures

In Menindee, New South Wales, millions of dead fish have been found in the Darling River. Local authorities and scientists say the die-off event is likely due to high temperatures and low oxygen levels as water from recent floods recedes.

The dead fish are primarily bony herring, or bony bream, and also include murray cod, carp, golden perch and silver perch.

“These fish deaths are related to low oxygen levels in the water (hypoxia) as flood waters recede,” the New South Wales Department of Primary Industries posted on Facebook. “Significant volumes of fish including Carp and Bony Herring, nutrients and organic matter from the floodplain are being concentrated back into the river channel.”

According to the Department of Primary Industries, the area has experienced widespread flooding. As the flood waters recede, oxygen in the water depletes. The situation is worsened by a local heat wave, which causes fish to require more oxygen, but the warmer water holds less oxygen.

The department noted that bony herring population tends to ‘boom’ during floods and often then sees significant decrease as flood waters recede, especially as this species is more vulnerable to low oxygen levels and high temperatures. Similar incidents happened in 2018 and 2019, Reuters reported, where thousands of fish died from extreme temperature changes and poor water quality.

The region has been dealing with high temperatures and flooding, and residents are now grappling with the sight and smell of dead fish in the local river.

“We’ve just sort of started to clean up, and then this has happened, and that’s sort of you’re walking around in a dried-up mess and then you’re smelling this putrid smell. It’s a terrible smell and horrible to see all those dead fish,” said local resident Jan Dening, as reported by NBC News.

Locals are also concerned about potential health impacts of the dead fish in the river.

“The stink was terrible. I nearly had to put a mask on,” local nature photographer Geoff Looney told NBC News. “I was worried about my own health. That water right in the top comes down to our pumping station for the town. People north of Menindee say there’s cod and perch floating down the river everywhere.”

The Department of Primary Industries said that multiple agencies were working to respond to the fish deaths, and locals were urged to call 1800-043-536 to report any relevant observations.