"The Nationals have at best dragged their feet on agreed concessions between the Commonwealth and the state, and at worst presided over a corrupted river system," he said.

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Claims of water theft in the Barwon-Darling system are now before the courts. The Berejiklian government was forced to launch a slew of inquiries into mismanagement and non-compliance in the northern region of the basin after an ABC Four Corners program last July.

'Playing politics'

Niall Blair, NSW Water Minister, called on Thursday for NSW Labor to decide whether it supported the plan's changes, and called on it to "stop playing politics with the livelihoods of NSW communities".

“NSW Labor needs to decide whether it remains part of a double act with the Greens, or whether it backs its federal counterparts and the important work the Basin Plan seeks to achieve,” Mr Blair said in a statement.

Qualified support

NSW Labor, though, is only willing to provide qualified support for the amendments, with a particular concern that the Menindee Lakes System will be destroyed "to benefit upstream irrigators".

"NSW Labor has not changed its position that the [Turnbull] government’s plan to augment the lakes risks destroying a major fish spawning area and permanently cripple a much-needed recreation and tourism area for Broken Hill," Mr Minns said.

According to a report by The Australia Institute last week, the proposed Menindee Lakes project was among the largest but also most controversial of the 36 projects supposed to provide 605 billion litres of annual water savings offsets in the southern part of the basin.

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The Menindee Lakes Water Savings project, which would supply 106 billion litres of the proposed savings, may even be unlawful because the benchmark model run was not adjusted as required. There were also detrimental impacts on water reliability that have not been offset or negated, the institute's Maryanne Slattery wrote.

The project, too, may have involved a conflict of interest because the consultant who prepared the project also sat as a member of the independent expert panel commissioned by the Murray Darling Basin Authority (MDBA) to review the effectiveness of a package of supply measures, the institute said.

A spokeswoman for the MDBA said the panel was "made up of experts in the field and all conflicts of interest are declared and managed".

Water Act changes

Fresh from its success in securing the basin plan amendments, the federal government is expected to table legislation on Thursday to amend the Water Act that underpins the scheme.

“In accordance with our agreement with Labor, we will make a sensible amendment to the Water Act to effect the outcomes of the Northern Basin Review," a spokesman for federal Agriculture Minister David Littleproud said.