Millions of dead fish fill a river in Australia, videos show. What caused the die-off?

A small town in Australia has been subjected to an extreme smell for days after residents noticed dead fish piling up in their local river.

Millions of fish have bubbled up to the surface, creating a sea of carcasses floating across the water.

Local fishery officials have said the fish are part of a “large-scale fish death event” impacting the Lower Darling-Baaka, Australia’s third longest river.

The dead fish — predominantly herring, but also cod, perch and carp — are a casualty of a heatwave moving across the country that is putting “further stress on a system that has experienced extreme conditions from wide-scale flooding,” according to officials.

Locals of Menindee, the town closest to the dead fish, have shared videos of the layers of the pungent phenomena on social media.

“The Bony herring species typically booms and busts over time,” fishery officials said. “It ‘booms’ in population numbers and can then experience significant mortalities or ‘busts’ when flows return to more normal levels.”

But, officials believe the cause of the fish dying en masse is more than just natural population cycles.

When there are periods of decreasing rainfall and high heat, as the Australian region is currently experiencing, there can be incredibly low levels of oxygen in the water, leading to a condition called hypoxia.

“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,” officials said.

Police Assistant Commissioner Brett Greentree told the Associated Press that contractors had been hired to come and remove the fish in an effort to keep the town’s water supply clean.

“I’m certainly not making promises that all the millions of fish will be removed by contractors because that is really a logistical nightmare,” he told the AP. “I understand and acknowledge the smell and sights on the river – nobody wants to see that.”

Menindee has seen events like this before.

There were mass dying events for fish populations during severe drought in late 2018 and again in early 2019, NPR reported.

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