NSW and Victoria are threatening to walk away from the Murray-Darling Basin Plan if controversial changes to the strategy aren't passed in Canberra in a debate that has scrambled political alliances at a state and federal level.
NSW and Victorian Water Ministers Niall Blair (National) and Lisa Neville (Labor), together warned they would pull out of the deal if amendments to the Murray-Darling Basin Plan fail to get passed by the Senate.
"This is not a bluff," Ms Neville told reporters in Sydney on Tuesday.
The changes, proposed by the Turnbull government last year, would see a reduction in the amount of water returned to the environment in the northern half of the basin.
However, a disallowance motion by the Greens, backed by Labor and the Nick Xenophon Team, threatens to sink the government's plan.
Mr Blair said the Greens were undermining important reforms that would help fix a 100-year-old problem.
"If the disallowances are successful ... there is no point continuing with the Murray-Darling Basin Plan and the ministerial council process from a NSW point of view," Mr Blair said.
Ms Neville, who is now at odds with her federal colleagues, said the future of the plan now rested with the Senate.
"If these motions are disallowed it is a slap in the face to communities and a slap in the face to Victoria and NSW," she said.
"I'm urging every Senator to think carefully about the future of the plan, if they want to achieve viable regional communities, a healthy river, good outcomes for the environment, they must support these components of the plan."
Mr Blair said the disallowance vote would prevent $180 million from going towards the health of rivers and fish populations in northern NSW and Queensland.
He said it would also mean a further 221 Gigalitres of water buybacks in southern NSW.
"If those principles and the processes that go through the ministerial council are just going to be put on the scrap heap because of this politicking in Canberra, there is no plan," he said.
Federal Nationals Leader Barnaby Joyce last week accused the Greens and opposition of playing politics with the health of the Murray-Darling Basin.
"The only reason they are doing this is for a political reason, the political expediency of trying to create a wedge in South Australian politics so that people who are not aware of the issues involved can get basically sold this pup," Mr Joyce told the ABC.
"So the prize for this is ashes in your mouth because you've completely and utterly destroyed all the hard work we've put into (this) for such a long period of time."
South Australian Water Minister Ian Hunter said his state would continue to oppose the Federal government's proposed changes until "real commitments and real projects" were realised.
"Victoria and NSW are walking away from the promise they made in 2012 when 3.4 million Australians almost lost their drinking water and livelihoods," Mr Hunter said in a statement.