South Australia's Royal Commission into corruption in the Murray-Darling Basin has begun.
At Meningie on Wednesday, Premier Jay Weatherill said the appointment of Commissioner Bret Walker had been approved and his instructions finalised.
He will be required to report back to South Australia's Parliament by February 1, 2019.
"(The Murray-Darling Basin Plan) was about putting the river first, making sure the river got what it needed to be healthy, then making sure the other users of the river respected the river," Mr Weatherill said.
"It couldn't be a more important agreement for our state or our nation.
"There are now questions about whether the spirit or intent of that agreement has been upheld by the upstream states."
He said Mr Walker was one of the most highly regarded barristers in the nation, and that his findings would be "cogent", "important" and respected by all.
"We want to get an outcome," the premier said.
"We don't want some thumping great document that sits on a shelf."
He repeated his belief that Mr Walker had the legal power to compel witnesses from interstate to cooperate with the inquiry.
Tony Burke, who was federal Water Minister when the basin plan was signed in 2012, said the Royal Commmission was critically important.
"The integrity of the baisn plan isn't just important for people at this end of the Murray-Darling Basin, it's important for irrigators doing the right thing, it's important for communities, it's important for ecology, it's important for traditional owners," he said.
"Today we're one step further towards making sure integrity will always be there for the Murray-Darling Basin Plan."
Speaking in Murray Bridge, Liberal Opposition Leader Steven Marshall said he supported the Royal Commission.
"We need to get to the bottom of these very serious allegations that SA has been dudded," he said.
"Let's get on with it."
SA Best candidate for Hammond Kelly Gladigau told The Standard she agreed the Royal Commission had to happen.
"As an irrigator, they play with us every year, depicting what we can get and changing their mind," she said.
"It does need to be sorted and we do need to secure our allocation in SA."