Labor and the Greens are urging the government to dump a cap on water buybacks for environmental use in the Murray-Darling Basin.
The federal opposition wants to repeal the 1500 gigalitre cap on buybacks for environmental watering in response to a scathing royal commission report, with the Greens supporting the move.
"We've seen the River Murray, the Darling absolutely crippled by mismanagement, water theft and a failure to implement the objectives of the Murray-Darling Basin Plan," Greens environment spokeswoman Sarah Hanson-Young told parliament on Tuesday.
Liberal frontbencher Anne Ruston accused the two parties of throwing a political time bomb ahead of this year's federal election.
She warned more uncertainty could risk a state government in the river system walk away from the plan.
"If you poke the bear one too many times, one of our constituencies that have to stay at the table to get this plan delivered will walk away and blow the whole plan up," she told parliament.
The South Australian senator said the cap hadn't been reached and buybacks would "rip the guts" out of communities if water allocations were changed.
Deputy Labor Senate leader Don Farrell said the cap reduced incentive for governments to buy back water for the environment.
"Because of the incompetence and misuse of the plan by the coalition government, we are now of the view that the only way to save the Murray-Darling Basin is to repeal that cap on the buybacks," he said.
Centre Alliance's two senators will also support a bill to dump the cap, which Labor wants to introduce to parliament on Tuesday evening.
SA Premier Steven Marshall is continuing to call for a meeting of Australia's water ministers to consider SA's royal commission which found allocations in the basin were determined by politics.