Hundreds of thousands of native fish die after heatwave
Updated ,first published
More than 100,000 native fish died in Lake Menindee in western NSW following last week’s heatwave; This was the first major fish kill in the lake since 2023.
Luke Driscoll, chief executive of Barkandji Native Title Group Aborigin Corporation, said at least 100,000 bony bream had washed up dead on the shores of Lake Menindee, near homes on the Sunset Strip. He predicted many more fish would die and sink to the bottom of the lake.
“This is a really bad smell for the people who live here. [the town of] “The Sunset Strip,” Driscoll said, “smells worse than the Menindee caravan park, two miles as the crow flies from Sunset.”
Menindee is one of the nine lakes that make up the Menindee Lakes south-east of Broken Hill.
Menindee Lakes and Darling-Baaka River witnessed mass fish kills in 2019 and 2023; Tens of millions of fish died because they could not escape the extremely shallow and hot waters.
Barkandji rangers have been on high alert throughout the heatwave after finding dead fish in the Darling-Baaka River below the lake last week. Driscoll said they found 400 to 500 dead fish, mostly carp, over four days last week, but by the weekend the crisis appeared to be over.
“I thought we dodged bullets,” he said. There were no dead fish at the boat ramp on the Sunset Strip on Saturday morning, but the situation changed dramatically over the weekend.
Driscoll said native freshwater sea bream cannot cope with the sudden change in temperature. After the extreme heat wave throughout the week, there was a storm and sudden coolness on Saturday night.
In Broken Hill, where Driscoll is located, the temperature was 40 degrees at 8.30pm on Saturday, then dropped to 22 degrees in less than an hour.
Professor Fran Sheldon, a Wentworth Group member and Head of Griffith University’s School of Environment and Science, said bony bream were particularly sensitive to heat, but the biggest reason behind mass fish deaths was lack of oxygen.
“There have been relatively good flows in and out of the Lower Darling [the] Over the past few years the fish have increased in the Menindee Lakes,” said Sheldon.
“Their numbers are larger, and as the river dries, it dries out because flows are reduced, fish concentrate in smaller volumes of water, and you end up with more fish than the body of water can support.”
Water NSW also issued a red alert for blue-green algae in Lake Menindee in January based on satellite imagery, later confirmed by water tests. Sheldon said the algal bloom will further stress the fish by sucking oxygen from the water at night.
Sheldon, who is involved in the government investigation into the 2019 fish kill, said the Commonwealth water owner had been sending more environmental flows into lakes and rivers in the past few years, but it was unclear whether that was enough to keep the river healthy during a prolonged drought.
Driscoll said Menindee rangers were working with the local council, the NSW Environment Authority and other government agencies to clean up the area around the lakeshore, and rangers from Wilcannia and Wentworth were also on hand.
Once the emergency cleanup is completed, rangers will test the water quality with a boat, Driscoll said.
“The rivers and lakes have been sick for a long time, and we’ve been seeing the effects for the last eight years,” Driscoll said.
“It’s sad because rivers and lakes are a big part of the Barkandji’s cultural history – Barkandji means ‘people of the river’ and this is their mother, their lifeblood, so to see their fish die – and the bony bream is a totemic species – really hurts those who live in the community and the whole Barkandji nation.”
Fish kills most commonly occur in lakes and rivers during heat waves or droughts; however, it can also occur in oceans, especially in aquaculture environments. More than four million salmon will die in Tasmanian fish farms in 2025, according to mandatory reporting to the state’s EPA, as a marine heatwave stresses fish and makes them more susceptible to disease.
Mass killings of wild fish in oceans are less common because fish are less crowded, but in January 2025 nearly 30,000 dead fish, including mackerel, bream, emperor, cod, wrasse and puffer fish, washed up on Western Australia’s Pilbara coast after a prolonged marine heatwave.
More recently, at Ballina in March 2025, hundreds of thousands of fish including bream, flathead and whiting died following flooding from former Tropical Cyclone Alfred.
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Caitlin Fitzsimmons is the environment and climate correspondent for The Sydney Morning Herald. He was previously a social affairs reporter and Money editor.Connect via email.
