Premier Jay Weatherill has written to Prime Minister Malcolm Turnbull calling for the investigation following a Four Corners report on Monday which alleged that billions of litres of water earmarked for environmental flows had been taken out of the Murray Darling system by NSW cotton growers.

Bernardi says the Federal Government should appoint a former judge to report within 30 days and the government must then take the results of that inquiry to COAG.

“We’ve got to get to the bottom of this quickly,” he told ABC radio today.

“The minister, Barnaby Joyce, should get an independent judicial inquiry or appoint a former judge to report within 30 days.

“They then need to take it to COAG, say this agreement is broken, here are the facts or someone has rorted the system, and get a result.”

The allegations of widespread water theft in NSW, including tampering with water meters, have sparked outrage in downstream states after they were aired on the Four Corners program on Monday.

SA Water Minister Ian Hunter said he was shocked by the “colossal and rampant” extent of the alleged theft.

The NSW government has instigated its own inquiry, but Weatherill says that’s not good enough and amounts to the state government investigating itself.

He told ABC radio today that only a judicial inquiry would get to the bottom of what was going on in NSW and also offered to put SA’s irrigators to the same scrutiny if necessary.

“Our concern is that this is just the tip of the iceberg,” Weatherill said. “We’ve always had great suspicions about the upstream states… and their commitment to this plan.”

Weatherill said there needed to be a national system of oversight of the Murray Darling Basin Plan, to ensure its regulation and the enforcement of its rules.

He also sought to bring Prime Minister Malcolm Turnbull into the debate, pointing out he had promoted the Murray agreement during his time as environment minister in the Howard Government.

The Premier suggested there were elements in Turnbull’s cabinet who were opposed to the plan.

“If he wants to preserve its integrity he now has to step up and stand up against his right wing. He’s decided that he won’t stand up against them on coal, but he has to stand up against them on the River Murray.”

Federal Education Minister Simon Birmingham said he would be “very surprised” if the matter did not end up before an independent inquiry.

“We want to hear the NSW response and give them the right to respond first and see what they’re proposing,” he said.

“Then, of course, we’ll make sure that every state and territory has confidence in the pathway forward.”

– with AAP