Residents at Menindee are bracing for a fourth mass fish kill in the Darling River in about three months, as a new paper finds water savings in the Murray Darling Basin may be just one-tenth the amount modelled.

The NSW Department of Primary Industries has warned the arrival of a cold front after another heatwave in the region this week posed a "high risk" of another bout of widespread fish deaths.

Murray cod and other fish are turning up dead in the Menindee Weir Pool on the Darling River as authorities warn of a fourth mass fish kill in the region. Credit:Graeme McCrabb

Possibly millions of fish, mostly bony herring but also endangered perch and Murray cod, were killed in the three previous events. A sudden drop in dissolved oxygen levels - as blue-green algae died and began decaying - was the prompt for the previous fish kills.

"They're super-stressed. It takes less [to kill the fish]," Graeme McCrabb, a Menindee resident, said on Tuesday. "The numbers of golden and silver perch and the cods got less [during each die-off]."