The vote was to have taken place at 9.30am but was delayed until night when the Greens, NXT and Labor voted against the regulation by 32 votes to 30.

NSW Regional Water Minister Niall Blair said that the move makes the basin plan untenable for NSW and urged the federal government to prevent the Senate’s vote from sabotaging the reform. 

The reform had meant a proposed cut from 390GL to 320GL that was recommended to the government following the Murray-Darling Basin Authority’s comprehensive review of the Northern Basin Plan.

The changes, proposed by the Turnbull government last year and supported by major irrigators in northern NSW and Queensland, 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, now threaten to sink the government's plan. NSW Water Minister Niall Blair said the Greens were undermining important reforms that would help fix a 100-year-old problem.

Victorian Water Minister Lisa Neville said the future of the plan rested with the Senate. Prior to the vote she said that the disallowance of the motions would be “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.”

An open letter to parliament, jointly signed by various irrigators and farmers organisations, has called on politicians to focus on the sustainability outcomes for the Basin.

“While not everyone in the Basin likes the Plan, everyone has been working towards achieving it and delivering a balanced plan,” the letter said. “[Wednesday] that hangs in the balance and we are concerned that we are on the verge of seeing the efforts of many thrown away compromising future environmental outcomes.”