Millions of fish that appeared floating dead in the waters of an Australian river this week are now being removed by authorities in a massive clean-up effort.
The huge carpet of dead fish appeared in the Darling River near the town of Menindee, situated around 580 miles west of Sydney, on March 17.
The fish, which are thought to have died en masse due to reduced oxygen in the river as a result of recent receding floodwaters, are thought to number around 20 million.
"It's like a slow funeral procession, it hangs over the town. Menindee doesn't wanna be known for this," one local told ABC News Australia in a video interview
The fish carcasses are being removed by contractors from South Australia, alongside Fire and Rescue NSW. Large rubber booms are being used to collect floating bodies, which will then be placed into landfill.
The NSW Department of Primary Industries (DPI) said in a statement that the fish deaths were likely caused by low oxygen levels from recent flood waters receding. This washed many tons of organic leaf matter into the riverway, which began to decay, with the decomposing bacteria using up much of the oxygen in the water. This, paired with the fact that the blazing temperatures in the region resulted in fish having a higher requirement for oxygen and, at the same time, water being able to hold less oxygen, led to the mass deaths of the river's fish.
Stock image of dead fish floating in Royal Lake Park in Fairfax, Virginia, alongside a goose. A river in Australia where millions of fish are floating dead is finally being cleared of the dead carcasses.Stock image of dead fish floating in Royal Lake Park in Fairfax, Virginia, alongside a goose. A river in Australia where millions of fish are floating dead is finally being cleared of the dead carcasses."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 DPI said in a statement. "The amount of dissolved oxygen water can hold decreases with increasing water temperature, which can add additional stress to fish that may already be struggling."
The fish were mostly bony bream but also included Murray cod, golden perch, silver perch and carp.
Mass fish deaths can be caused by a number of other environmental issues, including chemical pollution and algal blooms. Similar die-offs have occurred in this region of the Darling River before, notably in 2019, where around 1 million fish died due to a massive algal bloom that also sapped the oxygen from the river waters.
Algal blooms may also lead to mass deaths by producing toxins that actively kill the fish, which is what is currently occurring in Florida. There, a red tide algal bloom is killing thousands of fish by producing a neurotoxin called brevetoxin. A similar red tide has been detected at a beach in Hong Kong today, mere miles away from another similar fish die-off event.
In Menindee, the river is slowly returning to its fish-free state.
"The poor people of Menindee—who have not only had to put up with the floods recently, they have had a really tough time—and now all these decomposing fish, you know, it has been really tough for that community," New South Wales Police Commander Brett Greentree said on Monday. "I really feel for them."
Locals are concerned for the quality of their tap water in the aftermath of the fish clogging up the river, and are shipping in clean drinking water.
"The results of current testing by Essential Water have confirmed the quality of the water has not been impacted and it's safe for customers to drink," Greentree said in a police statement.
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"There are multiple viable solutions to maintain water supply and increased monitoring and testing will ensure changeover is immediate if alternative supply is required," he said.
"Residents in the Main Weir pool whose properties ordinarily rely on the river for water supply can access water carting for their domestic use by contacting Central Darling Shire Council."
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