Loading The advice from Fisheries NSW was issued after it reviewed a draft version of the 2012 Barwon Darling water sharing plan and described the river system as a "key fish habitat". It flagged concerns the draft plan was based on a series of outdated flow classes developed over a decade earlier, even though river flows had plunged by as much as 73 per cent in some areas since then. On Sunday NSW Opposition Leader Michael Daley seized on the document as proof the mismanagement of the river system was to blame for recent fish kills, which he slammed as a "an international embarrassment for Australia". "It didn't need to be this way," he said. "The document says that if the government proceeds with its water sharing plan and allows more water to be sucked out of those rivers, it will hurt ... the fish and the aquatic life in those river systems."

Labor called on Prime Minister Scott Morrison to gather an independent team of scientists to urgently investigate the fatalities. But the Minister for Primary Industries Niall Blair hit back, pointing out the government had implemented the changes recommended by Fisheries NSW. As suggested by the agency, the final version of the water sharing plan included a clause allowing for a review of flow classes and water access rules should a study show they were having an adverse impact on threatened fish species. However a government spokesperson confirmed to the Herald that such a review was never carried out, because it was not deemed necessary until the mass fish kills of recent weeks. "The recent Menindee fish kill was unprecedented ... it was caused by a perfect storm of events," Mr Blair said.

Loading Professor Richard Kingsford, the director of the Centre for Ecosystem Science at the University of NSW, said the emergence of the 2012 document was "not at all surprising". "Generally water legislation in NSW and in other states has pretty much ridden roughshod over environmental values both within government and outside government ... this is just another in a long history of that happening," he said. The death of up to one million fish at Menindee, in the NSW far west, has been described as one of the largest fish kills ever recorded. Mr Littleproud said he had asked the Murray-Darling Basin Authority to gather state and federal water managers this week to look at “the immediate risk of further fish kills and how we can mitigate that risk, including through the release of environmental water”.

They would also consider whether environmental water priorities need to be adapted and would advise Mr Littleproud on what else could be done to avoid and respond to deaths. “The fish kills we’re seeing are terrible. NSW data reveals there have been 600 freshwater fish kills in NSW since 1980, and we should expect more next week,” he said. He said he’d offered NSW “any assistance it requires as it responds to these incidents, and to rebuild fish stocks when it rains” and announced $5 million for a native fish management and recovery strategy that would come from MDBA coffers. There has been a war of words over whether the NSW government is partly responsible for the environmental catastrophe, due to the over-allocation of water to lobbyist irrigators. Mr Littleproud blamed drought for the mass deaths that have shocked farmers and environmentalists in recent weeks.

Loading The immediate trigger for the incident appears to have been a cold snap that killed blue-green algae, which in turn caused oxygen levels to plummet. In a letter sent on Sunday to Mr Morrison that raises the political stakes on the issue, Opposition Leader Bill Shorten said the scientific taskforce should report to Federal Parliament in its first sitting week in February. It should probe whether misuse of water in the river system has contributed to the deaths – reportedly one of the worst mass fish deaths on record. “This is an ecological disaster and an unfolding emergency and should be treated as such,” Mr Shorten said.