More than 10,000 mortalities along a 40km stretch of the Darling River were discovered by the department.

As well as at the Darling River at Menindee, fish kills have occurred at the Namoi River below Keepit Dam and the Lachlan River at Wyangala Dam.

DPI aquatic environment director Sarah Faifull said the prolonged dry period had resulted in poor water quality along much of the Darling River and in other valleys.

“Algal alerts have been in place for several weeks in the Menindee region and linked to this, low dissolved oxygen levels are likely to occur within slow flowing or no flow sections of the river,” she said.

“The impact of intense rainfall events after very hot conditions, similar to that experienced last week at Menindee, can exacerbate water quality concerns by mixing remaining water in riverine pools and disrupting algal blooms, further reducing the oxygen available for already stressed fish.

“Investigations by district fisheries officers from DPI revealed over 10,000 fish mortalities along a 40km stretch of the Darling River, including numerous Murray cod, golden and silver perch, and native bony bream.

“The rising temperatures across the state and low river flows place significant pressure on water quality, with similar events occurring at Wyangala Dam, affecting carp and native species and below Lake Keepit, where thousands of native fish have died.”

WaterNSW continues to monitor water quality throughout the dams and river systems.

“The result [of intense drought conditions] is record low inflows into some major dams and cease-to-flow conditions in many rivers and creeks, with climbing summer evaporation rates placing further pressure on falling supplies,” WaterNSW systems operations executive manager Adrian Langdon said.

“As well as bringing hardship to local farmers and surrounding communities, the stressed river network is also impacting the riverine environment.

“These impacts are being felt most acutely in the form of declining overall water quality, blue-green algae outbreaks and fish kills.

“Without significant rainfall to generate replenishment flows, it’s is almost certain these impacts will persist and possibly increase further as summer proceeds.”

Fisheries staff advise local anglers and residents the current low flows and warming temperatures are likely to pose an ongoing threat to native fish throughout the summer.

Community members are encouraged not to be alarmed and to report any similar incidents or observations through the Fishers Watch hotline on 1800 043 536.