There are concerns more fish will die with hundreds of thousands already killed off in far western NSW as the drought continues to grip the state.
The ongoing dry conditions and a recent big drop in temperature could be the cause of the mass death of fish in the Menindee region with investigations underway by the NSW Department of Primary Industries and WaterNSW.
The cool change may have disrupted an existing algal bloom, killing the algae and depleting dissolved oxygen, worsening the water quality for fish, DPI senior fisheries manager Anthony Townsend said,
The golden perch, Murray cod and bony herring are among the species affected in the Namoi River near Gunnedah, the Lachlan River at Wyangala Dam and the Darling River.
It follows an incident in December after intense rainfalls following a spate of hot weather resulted in more than 10,000 fish mortalities along a 40km stretch of the Darling River.
Mr Townsend warned the current low flows and warming temperatures are likely to pose an ongoing threat to native fish throughout the summer.
WaterNSW executive manager Adrian Langdon said it was "almost certain" the worsening water quality will continue and possibly increase as the hot weather persists without significant rainfall.
