Scientists say irrigators extracting excess water has contributed to the death of millions of fish in the Murray-Darling system.

An expert panel has handed down its report into three major fish kills at Menindee in far west NSW.

It found “serious deficiencies” in governance had “eroded” the value of the Murray-Darling Basin Plan and the Water Act.

The panel - formed at Labor’s request by the Australian Academy of Science - said the mass deaths were unusual in their severity, impact on large, older Murray cod and association with low flows.

Professor Craig Moritz said the deaths are the products of a river system in “crisis”.

“To me, it was like the coral bleaching event for the mainland,” Prof Moritz said.

“Our review of the fish kills found there isn’t enough water in the Darling system to avoid catastrophic outcomes. This is partly due to the ongoing drought. However, analysis of rainfall and river flow data over decades points to excess water extraction upstream.”

The expert panel recommends that urgent steps should be taken within six months to improve the quality of water throughout the Darling River.

“That should include the formation of a Menindee Lakes restoration project to determine sustainable management of the lakes system and lower Darling and Darling Anabranch,” Prof Moritz said.

The panel also recommends a return to the framework of the 2012 Murray Darling Basin Plan to improve environmental outcomes.

“The best possible scenario is water in the Darling all the way to the bottom and in most years. We are hopeful that this could be achieved if the panel’s recommendations are implemented,” Professor Moritz said.

Federal Agriculture Minister David Littleproud has maintained his view that a lack of rainfall caused the fish deaths.

“The reality is unless it rains there is no water that runs down the Darling,” he told Sky News on Monday.

“To say that anyone has maliciously done the wrong thing is dangerous, it is political and we don't need that.”

NSW Regional Water Minister Niall Blair alleges there were contradictions in the report and he would not back the recommendation to lift the cap on buybacks and repeal the Northern Basin review.