The most significant mass die-off of fish in decades has hit a regional New South Wales town. Initially reported on Friday morning, it is estimated to have affected millions of fish, according to the state’s river authority.
According to the NSW Department of Primary Industries, a heatwave triggered a mass death of wild fish on the Darling-Baaka river near Menindee. It was a result of an ongoing heatwave that is affecting the water system across western NSW.
Recent fish kills in the same region have been caused by blue-green algal blooms that deoxygenate rivers. These blooms are a natural response to environmental conditions such as farm fertilizer run-off, high temperatures, and low rainfall.
They can also occur due to wide-scale floods and lead to a sudden decline in oxygen levels that can suffocate aquatic animals.
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The current heatwave is causing a decline in oxygen levels in the water, and the number of dead fish is expected to increase in the coming days.
“There is an enormous wall of dead fish, tens of kilometers down the river,” said local Graeme McCrabb. He described the scale of the die-off as “unfathomable” and said he believed the rotting bodies would likely be too large to remove.
Locals say it’s the most significant fish death event to hit the town, which experienced another significant mass fish death just three years ago.
Residents in Menindee, about a thousand km (620 miles) west of Sydney, have complained of poor water quality and suffocating algal blooms in the past. However, the Department of Primary Industries has told the Herald it’s working with local communities to ensure the water quality in the Darling-Baaka remains healthy.
Earlier this year, the same area suffered a massive fish kill that killed about a million native fish in just one stretch of river. It was the largest in the area in the last decade due to blue-green algal blooms.
The department has urged residents to avoid swimming in the river. It also asks people to report any fish kills they see on 1800 043 536 or share them with the Environment Protection Agency.
In addition to the mass deaths, the Darling-Baaka has been clogged with debris and has seen little or no flow from its main tributaries. These factors contribute to the decline in fish populations and their lack of habitat.
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Despite efforts to restore river flows and oxygen levels, these factors deplete the system. Ultimately, the only thing that will prevent a return of fish kills is fresh water from flowing into the lower Darling Basin.
Fortunately, there’s been a considerable effort to improve the Murray-Darling river’s water quality over the past few years, including installing aerators to help maintain oxygen levels in refuge pools. However, the conditions that led to the recent fish kill at Menindee will inevitably return, and they’ll continue to impact the quality of the water supply in Menindee for years to come.