An environmental group claims a river in far western NSW, where up to a million fish have died, was in trouble before the drought because of water mismanagement.
The mass fish death in the Darling River system at Menindee Lakes has sparked an investigation by NSW DPI and WaterNSW.
Golden perch, Murray cod and bony herring are among the species affected.
NSW DPI said ongoing dry conditions and a recent big drop in temperature could have caused the large fish kill, but environmental group Inland Rivers Network says water mismanagement impacted the health of the river before the drought.
The group said the amount of water diverted for irrigation means the Darling River isn’t receiving the flows it should be getting.
‘‘The drought is an extreme drought but because any flows that might have got into the Darling River are being used somewhere else, it has exacerbated the problem,’’ president Bev Smiles said.
NSW Primary Industries and Regional Water Minister Niall Blair is ‘‘not happy’’ about the situation but said he does not have control of Menindee Lakes when they contain more than 480Gl of water as the flow is shared with other states.
‘‘We want to reconfigure those lakes through engineering solutions, and also talk to Canberra about the rules so we don’t keep pulling the plug and then not turning the tap on, so that we can have better outcomes,’’ he said.
Mr Blair said there had been no natural events replenishing the system, and the release of water had been at the call of South Australia, the Murray-Darling Basin Authority and the Commonwealth Environmental Water Holder.
But independent MP Jeremy Buckingham said the NSW Government and MDBA’s ‘‘rapid’’ draining of the lakes network had been to spare upstream corporate irrigators from contributing more water to the environment.
He warned the Darling River and the fish that live in it would die if water management of the Murray-Darling Basin was not overhauled.
MDBA chief executive Phillip Glyde said drought was to blame.
‘‘The recent tragic fish deaths in the lower Darling are a terrible reminder of the effects drought can have on our environment,’’ Mr Glyde said.
‘‘Unfortunately, the main causes of this distressing event are the lack of water flowing into the northern rivers and the impact of 100 years of over-allocation of precious water resources throughout the entire basin.’’
National Irrigators’ Council chief executive officer Steve Whan said the Murray-Darling Basin Plan was necessary.
‘‘It is always difficult to see large fish kill events — whether they are from drought, algal events or black water,’’ Mr Whan said.
‘‘Unfortunately, in nature they are not always avoidable but we should do our best to minimise their occurrence.
‘‘That’s why the Murray-Darling Basin Plan is important.
‘‘It’s about managing a scarce resource, shifting water from agriculture to the environment and responding to times of drought.’’
The latest kill follows an incident in December, when intense rainfalls after a spate of hot weather resulted in more than 10000 fish deaths along a 40km stretch of the Darling River.