Mr Walker wrote that current senior management of the authority and its board showed"gross negligence"and"maladministration"in failing to ensure the basin plan was lawful with respect to addressing climate change.
The report said the authority failed to act on the best available scientific knowledge when determining how much water should be recovered for the environment across the basin,saying the decision was based on"politics rather than science".
The authority failed to disclose modelling used to make its decisions and"completely ignored"climate change projections when expert evidence suggested the reduction in water run-off could be"catastrophic".
The report said the causes of the shocking fish kill at Menindee Lakes had not been determined at the time of writing.
Illustration:Matt GoldingCredit:
However it described as"grossly irresponsible"public comments by NSW Water Minister Niall Blair,who after the disaster said the Menindee Lakes Project must proceed and not doing so would"blow up"the basin plan. The controversial scheme involves reducing evaporation in the lakes by making them smaller.
"It amounts to saying that NSW will do what it can to destroy the plan if this particular highly problematic project is not guaranteed,in advance,to contribute to a reduction in environmental flows and a commensurate increase in irrigation take,"the report said.
It also described as"gross maladministration"the authority’s recommendation that the federal government reduce by 70 billion litres the target amount of water that irrigators must return to the environment in the northern basin,covering Queensland and part of NSW.
The authority said the move would save about 200 jobs in irrigation-dependent communities.
The report called for"an independent,scientifically astute and experienced body responsible for auditing the effectiveness of the implementation of the basin plan",saying the authority had until now been"marking its own work".
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New determinations of how much water could be extracted for irrigation should be made urgently,ensuring the health of the environment was prioritised,it said.
In a statement,the authority said it was confident the plan was made lawfully and was based on the best available science,saying it had"extensive documentation"to support this claim.
"The MDBA rejects any assertion by the commission that it has acted improperly or unlawfully in any way,"the statement said,adding that the plan was enacted with bipartisan support from state and federal governments.
The authority said the plan was at the halfway mark and"it is vital that this work continues".
Federal Agriculture and Water Resources Minister David Littleproud said the government would consider the report,but that"significant inroads"had been made in restoring water flows and improving compliance.
"The legal advice to the Commonwealth government under both sides of politics for the last seven years has been consistent — the basin plan is lawful and was lawfully made,"he said.