The northern part of the Murray-Darling Basin will be flushed with gigalitres of environmental water as the NSW and Commonwealth governments attempt to prevent the long-suffering rivers drying out.
Water has stopped flowing in some parts of the Barwon-Darling system in NSW's northwest while other tributaries are in decline amid extended hot and dry weather.
Fish populations, including the Murray cod, are being placed under threat while farming communities have faced water restrictions.
The Commonwealth and state governments on Monday jointly committed to releasing more than 30 gigalitres - 23 from the federal government and seven from NSW - for environmental flows from mid-April.
"We know how important the Barwon and Darling rivers are to our most remote communities and this event will refresh those rivers after a long period of hot and dry weather," NSW Regional Water Minister Niall Blair said in a statement.
The water is needed to maintain a connection between the northern rivers and the Barwon-Darling, the Commonwealth Environmental Water Holder Jody Swirepik said.
"Although our purpose is to improve river health, we do hope it will also relieve some of the pressure the community has been feeling," she said in a statement on Monday.
The governments hope the water release will capitalise on rainfall feeding the northern parts of the basin and the offer by some Queensland irrigators not to take water.
The recently-retired former environmental water holder, David Papps, was far from impressed and said basin states committed to implementing the basin plan in full, not just "the bits that suit their political agenda".
"In my opinion, NSW has actively undermined the plan's environmental elements. Aided and abetted by Victoria," he wrote on Twitter on Sunday.
"They continue to do so."
Australia's environmental history was "littered" with irrational political decisions, Mr Papps added.
The Murray-Darling Basin Authority in late 2017 slammed NSW and Queensland for not forcing irrigators to comply with the basin's water management plan.
But the authority on Monday applauded the NSW government's commitment to protecting the "important flows" and working to get the balance right between competing needs for water.
"We welcome the immediate steps taken by NSW to protect these flows in the short term, by issuing a ministerial order to ensure the water is not pumped and makes it through the system," MDBA executive director Peta Derham said in a statement.
The water will be released in mid-April and is expected to have completed its 2000-kilometre journey to Wilcannia by late May.