The South Australian Government has refused an offer from the Murray-Darling Basin Royal Commission to investigate recent fish kills in the lower Darling River.

Key points: Murray-Darling royal commission report to be published in full on February 1

Murray-Darling royal commission report to be published in full on February 1 SA Attorney-General Vickie Chapman refuses request to investigate recent Darling River fish kills

SA Attorney-General Vickie Chapman refuses request to investigate recent Darling River fish kills Crossbench MPs say push for a delay related to NSW state election

But the state's Attorney-General, Vickie Chapman, has bowed to pressure from royal commissioner Bret Walker SC to keep the commission's website operating for 12 months after his report is published.

The commission is due to deliver is final report to SA Governor Hieu Van Le on February 1, and has said it will include "adverse assessments of many governmental decisions and processes".

This morning, Mr Walker took the unusual step of releasing letters between the commission and the Attorney-General's Department, revealing a dispute over how and when his report should be published.

The letters revealed the commissioner had requested in November to have his report published in full on his own website immediately after it was handed to the Governor.

But the request was refused, with the Government insisting it would instead be published on the Environment Department's website.

Further, the commissioner was advised that his own website, which contains transcripts, submissions and other evidence, would be shut down on March 30.

Commissioner wants report published immediately

In a strongly worded response to Ms Chapman, Mr Walker urged "immediate and complete publication of the report".

Bret Walker SC has had several disputes with Attorney-General Vickie Chapman. ( ABC News: Matt Roberts )

"It is my view that the whole report should be published immediately," the letter stated.

"The public interest demands it. There are no countervailing considerations such as national security or the administration of justice.

"The national implications of the report's subject matter are also a reason for the report to be made available for consideration and criticism without delay."

Mr Walker's letter also urged the Government to keep the commission's own website online for longer, so readers could check his findings against lengthy and complex documents and transcripts given in evidence.

"This is all the more important because my conclusions include adverse assessments of many governmental decisions and processes," the letter said.

"The criticism and justification of governmental conduct is peculiarly, in our society, best done openly."

Fish kills will not be investigated

In the letter, Mr Walker volunteered himself to investigate recent fish kills in the lower Darling and various political, official and community responses to them.

"If the Government were interested to investigate these matters in relation to the proper concerns of South Australia in them, I would be willing to accept an appropriately tight, limited and economic extension of the time for a final report, so as to encompass these recent events in my work," the letter said.

But Ms Chapman today declined the offer of an extension.

"I note that the cost to date of the commission is $5.017 million," she wrote.

"Extending the royal commission would be an unfair burden on South Australian taxpayers given the sum already spent."

Millions of dead fish continue to rot in the Darling River at Menindee and downstream. ( Facebook: Debbie Newitt )

Ms Chapman did not indicate when the Government would publish the report, but agreed to keep the commission's website operative for 12 months.

"Given how strongly you have expressed the need for the commission's website to remain operative for some time, I do not propose to quibble about the matter," she wrote.

In her letter, Ms Chapman asked the royal commissioner to advise whether he had referred any matters to investigative or prosecutorial agencies.

'Protection racket' ahead of NSW election

Mr Walker was appointed as royal commissioner in 2017 at the behest of then-South Australian Premier Jay Weatherill, soon after the ABC's Four Corners program aired allegations of upstream water theft.

The commissioner engaged in a separate dispute with the State Government last year, after it refused to grant his request for an extension, and abandoned a legal push to force Commonwealth public servants to give evidence.

Crossbench senators have used the latest disagreement to accuse the South Australian Liberal Government of running a "protection racket" for Liberal governments elsewhere in the country.

South Australian Greens senator Sarah Hanson-Young said the suggestion the report may not be released immediately showed a contempt for the public.

"The South Australian Government should not be running a protection racket for their federal counterparts and release this report immediately when the commissioner delivers it," she said.

"It's political interference like this that warrants a federal royal commission as a matter of urgency."

Centre Alliance senator Stirling Griff questioned whether the SA Government may be seeking to delay the release of the report beyond the NSW election on March.

"This is not a political issue. It should not be a political issue," he said.

"If they are trying to delay it beyond the New South Wales election, I think everyone will see through that."

State Opposition Leader Peter Malinauskas said whether the Premier delayed the release of the report or not would be "a key test of whether Steven Marshall is standing up for South Australia and the Murray or taking his orders from the eastern states".