NSW Primary Industries Minister Niall Blair argues the mass fish death could be due to ongoing drought conditions followed by a recent drop in temperature which killed the algae and depleted the dissolved oxygen in the Darling River system at Menindee.

The Murray-Darling Basin Authority authorised a water release from the Menindee Lakes to South Australia and because of the drought there was no water to replenish the system, Blair says.

The minister today inspected the river and was confronted by more than 100 angry residents demanding answers.

Rob McBride, a grazier who lives about 40 kilometres south of Menindee on the Lower Darling, insists the deaths have nothing to do with the drought and instead are the result of a “man-made engineered disaster”.

“It has everything to do with the total mismanagement and corruption of the water system,” McBride told AAP on Wednesday.

“The blue-green algae will take over each stretch of the 600km river and it will kill billions of fish. It’s a collapsing ecosystem.”

McBride posted this video on his Facebook page yesterday, which has since attracted more than two million views.

The Menindee Lakes, which are about four times the size of Sydney Harbour, were drained twice in four years and are now sitting at between 2.6 per cent and four per cent capacity, he said.

His daughter, Kate McBride, says the deaths are due to the diversion of water from the river for irrigation and the draining of Menindee Lakes.

“These huge Murray cods are about 80 years old, they’ve survived the drought and extreme weather, but the one thing they can’t survive is this draining,” she said.

The latest kill follows an incident in December resulting in more than 10,000 fish mortalities along a 40km stretch of the Darling River.

A South Australian royal commission was held in 2018 to investigate allegations of widespread water theft from the Murray-Darling Basin by rogue irrigators with its report expected on February 1.

– AAP