Officials say the die-off likely occurred as fish need more oxygen in hot weather, but oxygen levels in the water dropped after recent floods receded.

Mass fish kills have been reported on the Darling River in recent weeks.
Mass fish kills have been reported on the Darling River in recent weeks. (AA)

Contractors are being hired to remove millions of rotting fish from a river in the Australian Outback after a unprecedented die-off following floods and hot weather, police have said.

Police Assistant Commissioner Brett Greentree said on Monday keeping the town’s water supply pure was the main priority and removing the dead fish was the next most pressing issue. 

Trained contractors had been contacted about removing the fish with nets, but 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,” Greentree said.

“I understand and acknowledge the smell and sights on the river — nobody wants to see that,” he added.

READ MORE: 'Unfathomable': Millions of fish die in Australian river due to heatwave

Insufficient oxygen

Authorities were supplying potable water to residents who rely on river water, which was continually being monitored for quality, Greentree said.

Tens of thousands of fish were found at the same spot in late February, while there have been several reports of dead fish downstream toward Pooncarie, near the borders of South Australia and Victoria states.

Enormous fish kills also occurred on the river at Menindee during severe drought conditions in late 2018 and early 2019.

Greentree said the current death toll appeared to be far larger than the events in 2018 and 2019.

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Source: AP