Australia's Murray-Darling Basin Authority acted unlawfully and water allocations must undergo a complete overhaul across the system, a South Australian royal commission has found.
The commission report released on Thursday found river allotments were driven by politics and accused the basin authority board of maladministration over its disregard for science.
It said water levels must be made on a scientific basis and in accordance with reconstructed water laws.
It also wants uniform penalties between basin states for irrigators who don't comply with regulations.
The South Australia-based royal commission's 736-page final report includes 111 findings and 44 recommendations aimed at improving the effectiveness of the Murray-Darling Basin Plan.
The Murray-Darling Basin Authority acted unlawfully when it "completely ignored" climate change projections for the determination of water allocations, it said.
"The (sustainable diversion limit) ignores the best available scientific knowledge."
"As an administrative decision, it is indefensible."
South Australian Premier Steven Marshall said the commission had strayed from its initial aim.
The Liberal leader vowed to look at the legality of the plan and respond later in the year.
Mr Marshall will ask Prime Minister Scott Morrison to convene a meeting of the Basin states to look at the inquiry findings.
"I don't want to be drawn on providing commentary at this early stage," the premier told reporters in Adelaide.
"But I can assure every single person in this state, we are taking this royal commission report extraordinarily seriously."
He said the inquiry had not focused on allegations of water theft in the basin, despite his Labor predecessor promising it would.
SA Water Minister David Spiers was disappointed with the commission's criticism of his actions, which were labelled a "capitulation" to the commonwealth contrary to the interests of the state.
"It is an isolated comment that doesn't consider all the other things that occurred," he said.
He said the government had got 450 gigalitres for the environment and $70 million for the Coorong river.
The South Australian government reiterated the need for the Murray-Darling Basin Plan to be delivered in full, along with 3200 gigalitres of water to SA.
“My government is committed to implementing the full MDB Plan and will demand every drop of the 3200gL of environmental flow agreed by the Commonwealth and Basin States in 2012 be delivered,” Mr Marshall said.
he said the health of the MBD was “critically important” to the tens of thousands of South Australians who lived and worked along the River Murray.
He said there was a shift in the focus of the Royal Commission.
“I note that when the Royal Commission was announced by the former state Labor government, South Australians were told the Commission’s focus would be investigating allegations of water theft in the MDB,” he said.
“This was not by any means the focus of this inquiry.”
To date, South Australians have paid $5.062 million to conduct the MDB Royal Commission, with that figure expected to rise once final payments are made but still remain within the $8.5m budget.
Read the full report here.