One of Australia’s foremost lawyers has issued an extraordinary warning that the Murray-Darling basin plan is likely to be unlawful because the authority overseeing it made a fundamental legal error when it set the original 2,750-gigalitre water recovery target in 2012.

Bret Walker SC, who chairs the South Australian royal commission into the Murray-Darling basin plan, issued the warning in a second issues paper. He also spelled out the far-reaching implications of the plan being unlawful.

Not only does it mean that the original water recovery target of 2,750GL was likely to have been set too low to deliver the environmental goal of the Water Act and could be challenged in court, but it also means that amendments to the plan now being debated by the Senate are likely to be invalid as well.

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These include a plan to trim 70GL from the northern basin water recovery targets and a suite of projects, known as the sustainable diversion limit adjustment projects, which would be funded in lieu of recovering 605GL in the southern basin.

Both are being strongly criticised by scientists and environmentalists because they believe that they further undercut the environmental outcomes of the plan. The Murray-Darling Basin Authority (MDBA) says it has relied on the best available science in recommending the changes.

The new uncertainty over the validity of the amendments will make it difficult for crossbenchers to support them as the Coalition government has urged.

Walker has provided a roadmap for environmental groups or an individual affected to challenge the plan in court.

At the heart of his advice is his view that the Water Act directs the MDBA to ensure environmental outcomes are achieved when it set the environmentally sustainable level of take (ESLT) from the river system. This is the flipside of setting the water recovery target.

But instead of considering the environmental outcomes only, the MDBA applied a triple bottom line approach, giving equal weight to social and economic impacts of water recovery.

“The MDBA also appears to have approached the word ‘compromise’ in the definition of ESLT in a manner involving compromise between environmental, social and economic outcomes rather than in relation to the concept of ‘endangering’ or ‘putting in danger’ environmental criteria such as key environmental assets, and key ecosystem functions,” the SA royal commission said.



“The commissioner is inclined to take the view that this approach to the word ‘compromise’ in s4 of the Water Act is not maintainable, or alternatively that he is presently unable to see how it is maintainable,” the paper says.

“There is also evidence that recovering an amount of water for the environment of 2,750GL does not, as a matter of fact, represent an ESLT in accordance with the definition of that term under the Water Act.”

Walker pointed to numerous reports, including a 2011 CSIRO report which said modelling based on a 2,800GL recovery target “does not meet several of the specified hydrological and ecological targets”.

There is also evidence that the MDBA received legal advice on more than one occasion, consistent with the commissioner’s concerns.

Murray-Darling: when the river runs dry Read more

In December 2010 the then head of the MDBA, Michael Taylor, resigned, citing the “challenges” of trying to comply with the Water Act while meeting the then Labor government’s insistence that he take account of social and economic impacts as well as environmental.



In his resignation press release Taylor referred to advice that said the MDBA “cannot compromise the minimum level of water required to restore the system’s environment on social or economic grounds”.

Walker also raises the possibility the Water Act and the Murray-Darling basin plan could also be unconstitutional because they rely on the commonwealth government’s external affairs power to enter treaties. In this case it is the Ramsar convention on wetlands and the biodiversity convention that Australia has signed, pledging to protect endangered environments and species.

The federal government has hinted that it will ask the new Liberal government of South Australia to wind back the royal commission’s terms of reference.