Experts fear whole populations of local native fish have been wiped out in the Lower Darling River.

Residents near the Menindee Lakes have reported a second major fish kill along a 20km stretch of water. It comes after an apparent mass event in December saw an estimated 10,000 fish die.

Local fish experts have warned that populations of Murray cod and other native fish could be wiped out if they keep dying at this rate.

They have also raised questions about the way WaterNSW is managing the lakes system.

Locals say the lakes were almost full two years ago, but since then WaterNSW has allowed the release of so much water and extraction upstream for irrigation that the lakes are now almost completely dry.

WaterNSW’s website shows the lake’s dam is about 3.2 per cent full.

The current concern is focused downstream from where about 10,000 fish were estimated to have died in mass death incident in late December.

The NSW Department of Primary Industries has since confirmed “a major fish kill event in the Darling river at Menindee affecting hundreds of thousands of fish, including golden perch, Murray cod, and Bony Herring”.

The DPI said the incident seemed to have resulted from a sudden drop in temperature during an existing algal bloom, leading to a depletion of dissolved oxygen in the river water, exacerbating poor water quality for already stressed fish.

WaterNSW and the NSW Department of Primary Industry both blamed the drought for the December deaths.

Local graziers have accused the NSW government of sacrificing their 500km stretch of the Darling to benefit upstream cotton growers, and blame the current crisis on WaterNSW’s decision to allow releases despite forecasts of drought.

A new plan for Menindee Lakes being considered by the Murray Darling Basin Authority proposes new projects that will deliver environmental outcomes without having to buy water for the environment from farmers.