Millions of dead fish have been found floating in an Australian river in New South Wales (NSW), with environmental officials attributing the deaths to depleted oxygen levels in the river following recent floods and hot weather.
The deaths occurred in the lower Darling-Baaka River near the town of Menindee on March 17, the NSW Department of Primary Industries (DPI) said in a statement on Facebook. The DPI stated that “millions of fish” were affected, predominantly bony herring and smaller numbers of other large-bodied species such as Murray cod, golden and silver perch, and carp.
“This event is ongoing as a heatwave across western NSW continues to put further stress on a system that has experienced extreme conditions from wide-scale flooding,” the department stated.
The DPI stated that the fish deaths were caused by hypoxia, or low oxygen levels in the water, which is believed to have occurred after flood waters receded.
“Significant volumes of fish, including Carp and Bony Herring, nutrients and organic matter from the floodplain are being concentrated back into the river channel,” it stated.
“The current hot weather in the region is also exacerbating hypoxia, as warmer water holds less oxygen than cold water, and fish have higher oxygen needs at warmer temperatures.”
Graeme McCrabb, a resident who spoke to The Guardian, described the magnitude of the fish deaths as “unfathomable.”
The decomposing dead fish could render the water unusable for residents, he said.
“The river is just white. I’m looking at probably a kilometer [a half mile] or a kilometer-and-a-half [almost a mile] of fish, and they’re all dead,” he told the media outlet.
Footage posted to Twitter by SBS shows a boat navigating through the mass of fish blanketing the entire surface of the river.
The incident follows fish deaths in the same area in 2018 and 2019, when up to a million fish died from poor water flow, poor water quality, and sudden temperature changes.
Joy Becker, an associate professor at the University of Sydney, said an investigation into the cause of mass fish deaths should be conducted as such events could occur when “the quality of the environment cannot sustain fish life.”
“It is important to remember that fish kill events impact not only the large-body fish like the Murray cod and bony bream but also the small-body fish like the gudgeons that are essential to maintaining a healthy aquatic ecosystem,” Becker said.
Police said on Monday that contractors are being hired to remove millions of rotting fish, but keeping the town’s water supply pure was the main priority. Dates for the work haven’t been set.
“I’m certainly not making promises that all the millions of fish will be removed by contractors because that is really a logistical nightmare,” Police Assistant Commissioner Brett Greentree said.
“I understand and acknowledge the smell and sights on the river—nobody wants to see that.”
Reuters contributed to this report.