Nationals MPs and senators this week launched two failed bids to scrap 450 gigalitres of water being returned to the environment under a dramatic proposal to shake up the Murray-Darling Basin Plan.

The Liberals stared down their junior coalition partner's rebellion despite the unusual attempt to force changes to an otherwise uncontroversial government bill improving compliance across the basin.

SA Water Minister David Speirs called for new Deputy Prime Minister Barnaby Joyce to reject his party's push to blow up the basin plan.

"A minority within the federal party, particularly Victoria and New South Wales, have decided to pitch this unusual idea based on voodoo science," Mr Speirs told ABC radio on Friday.

"They're behaving completely irresponsibly."

Nationals whip Damian Drum accidentally circulated his talking points in parliament when he launched the party's second failed push to change the government bill.

"The science no longer supports SA needing fresh water," the document said.

"Rising sea levels will mean the SA lower lakes system will not need environmental water."

Mr Speirs rejected the claims, saying evidence clearly supported water coming into SA for the environment and irrigators.

"It's one of those things you just shake your head at in absolute astonishment," he said.

"You have to laugh because what else could you do."

He said it was unbelievable a mainstream party of the federal government would make the statement.

The Nationals scheme would also have banned water buybacks and stopped more environmental flows after the plan's completion in 2024.

Government Senate leader Simon Birmingham - the most senior South Australian in federal cabinet - said attempts to radically overhaul the basin plan needed to stop.

"I've seen members cross the floor before and I expect I'll see members cross the floor again," he told the ABC.

"I also expect the government will remain resolute in its position of support for the Murray-Darling Basin Plan."

Senator Birmingham also rubbished suggestions his state would not need fresh water.

"No of course it's not true. Fresh water is essential for any civilisation. It's certainly essential for any city, state, any population centre," he said.

"I assume the points were probably trying to say additional water flows or additional water recovery were not essential."

He expressed deep disappointment with the Nationals but stressed he respected the rights of backbenchers to represent constituents.

Australian Associated Press