Recent fish kills in western New South Wales have put Australia's Murray-Darling Basin Plan back in the headlines.

Key points: SA's Murray-Darling Basin Royal Commission will deliver its findings today

SA's Murray-Darling Basin Royal Commission will deliver its findings today It is not clear when the SA Government will make them public

It is not clear when the SA Government will make them public The inquiry has been controversial

However, it has been at the forefront of some of Australia's top legal minds for the past 12 months, with the South Australian Murray-Darling Basin Royal Commission putting it under the microscope.

Commissioner Bret Walker has officially handed his final report to SA Governor Hieu Van Le this morning.

He will hand the report to the State Government later today.

It is expected to be released publicly after it has been before Cabinet on Thursday.

Commissioner Bret Walker has already foreshadowed that it will contain adverse assessments of "many governmental decisions and processes".

What is the Murray-Darling Basin Plan?

Management of Australia's biggest water resource has been contentious since before federation.

History was made in 2012, when Queensland, New South Wales, the ACT, Victoria and South Australia signed up to the national plan, but it remains controversial.

Some believe it does not provide enough flows to protect the environment, while communities dependent on irrigation say it threatens their economic future.

Why did SA decide to hold a royal commission?

Billions of litres were being diverted for irrigation, in breach of the deal. ( Four Corners )

In 2017, an ABC Four Corners investigation uncovered irrigators in New South Wales were taking billions of litres of water earmarked for the environment.

A subsequent report found poor levels of enforcement and a lack of transparency surrounding water management in New South Wales and Queensland.

That sparked outcry in South Australia, at the very end of the system and often the first place to feel the impact of low water flows.

Then premier Jay Weatherill said the report did not go far enough, and needed more detailed findings about individuals who had committed water theft.

He announced the Labor government would launch a royal commission.

Key players didn't give evidence

The Federal Government moved to block public servants appearing. ( ABC News: Nick Haggarty )

The SA Government came out swinging with its royal commission, but it didn't take long for it to be encumbered.

The Federal Government launched injunction proceedings in the High Court to prevent any Commonwealth public servants from giving evidence.

That included Murray-Darling Basin Authority (MDBA) staff, who are responsible for implementing the plan.

The Federal Government argued it was a longstanding legal precedent that state-based royal commissions did not have the power to compel federal witnesses.

Evidence of mismanagement and fraud revealed

While the royal commission could not hear evidence from current MDBA staff, it did hear from some former senior employees.

They included David Bell, who at one stage was responsible for setting an environmentally-sustainable level of water extraction.

He told the inquiry the amount of water set aside for the environment became a political decision, rather than a scientific one.

The 2010 'Guide to the proposed Basin Plan' recommended 6,900 gigalitres of water would need to be returned to the system for there to be a 'low uncertainty' of achieving environmental outcomes.

In the final 2012 plan, 2,750 gigalitres were allocated.

The commission heard the MDBA made "massive" and "crucial" errors. ( Emma Brown )

It also heard from Dr Matt Colloff, a now retired CSIRO scientist who was part of a team that worked on a report into the plan.

He told the commission his report was altered by CSIRO management, under pressure from MDBA staff.

In his closing submission to the royal commission, counsel assisting Richard Beasley SC said that by taking social and economic factors into consideration when setting environmental flows, the MDBA had erred.

"The Murray-Darling Basin Authority has misinterpreted the Water Act, not in a minor way, not in an unimportant way, in a crucial way," he said.

"That's not only error, or worse than error, it's a massive one with regrettable consequences for the lawfulness of that part of the Basin Plan."

The royal commission wanted more time

Commissioner Bret Walker has been at odds with Attorney-General Vickie Chapman. ( ABC News: Matt Roberts )

Between the establishment of the royal commission and the date it was due to report, South Australia had a change of government.

Commissioner Bret Walker wrote to the new Liberal Government, pushing for an extension of time while the case in the High Court played out.

The Liberal State Government knocked him back, in a stoush that led Mr Walker to demand an apology from Attorney-General Vickie Chapman, claiming she had made a public statement that was "wrong, discourteous and inappropriate".

Last week, Mr Walker asked for another short extension, this time to investigate the fish kills in the Menindee Lakes.

Again, he was knocked back.

Ms Chapman said it would be an "unfair burden on South Australian taxpayers".

What will happen now?

The commission wasn't given the time to investigate fish kills. ( Facebook: Debbie Newitt )

While the SA Government has said it will release the report "at the earliest opportunity", it is expected to be released publicly after it has been before Cabinet on Thursday.

The Government will first spend time putting together its formal response to the report's recommendations.

Ms Chapman said the report was also likely to be taken to the Council of Australian Governments (COAG) for the Prime Minister and other basin states to consider.