Despite Ms Pavey's criticism, the Murray Darling Basin Authority has backed Dr Keniry's recommendations in a submission yet to be released publicly but reviewed by the Herald. The NRC is an independent agency which advises the government on environmental issues including native vegetation, rivers, wetlands and soil. Parched land near Coonamble, in north-western NSW. Credit:Janie Barrett Ms Pavey's criticisms follow a difficult month for the Coalition, which has been beset by splits over the now-halted Essential Energy job cuts and acrimony over abortion reforms that do not have widespread support among many of Ms Berejiklian's Liberal colleagues. Tensions between the Coalition partners over water reforms have risen dramatically in recent weeks, with Environment Minister Matt Kean and Planning Minister Rob Stokes backing the NRC and telling colleagues they were committed to enacting the review's recommendations.

Ms Pavey and Deputy Premier John Barilaro are opposed to recommendations that would restrict when and how much water irrigators holding generous water allowances known as A-class licences can use. The NRC said the issuing of some of these licences by the Coalition in 2012 had pushed the river past Bourke into drought three years earlier than under normal circumstances. That conclusion was supported by technical modelling conducted by Griffith University academic Fran Sheldon, a researcher at the Australian Rivers Institute. The review was commissioned by former water minister Niall Blair after widespread fish kills and water shortages last year, with a draft report released late last month finding the Barwon-Darling was "an ecosystem in crisis" and upstream irrigators had been prioritised over other users. Loading In her letter to Dr Keniry, Ms Pavey writes that the work conducted by Professor Sheldon "was a hypothesis not tested as she did not have access to a Barwon Darling operations model".

"As the system operator for the state’s rivers, WaterNSW is the only agency with operational models for the Barwon Darling ... they advise that the NRC did not ask them for modelling information prior to the release of the draft report," the letter reads. "Further, the peer review was undertaken by academics who have a prior history of collaboration with Professor Sheldon, one with a history of research collaboration of almost twenty years and as recently as June 2019," the letter continues. "It creates a potential conflict of interest that should at least be declared and at best avoided." Ms Pavey's letter to Dr Keniry comes after WaterNSW supplied her with an analysis of the NRC's work which said the 2012 changes — allowing more water to be extracted by upstream irrigators — "had only a very small impact on the flows at Bourke over the past 2.5 year". "According to this analysis it is therefore wrong to say that upstream extractions during this period bought the drought forward by three years," the internal briefing reads.

But the NRC's executive director Bryce Wilde accused WaterNSW of "rapidly" undertaking modelling last week which was "scientifically flawed" and said the agency stood by Professor Sheldon. "Professor Sheldon’s work has been peer reviewed by two authorities in the hydrological field ... neither have any conflicts of interest with Professor Sheldon," Mr Wilde said. "WaterNSW's modelling was not available at the time of the NRC’s work and was undertaken rapidly after our work became public." "For a model to be scientifically robust it should be for a long time period, ideally from 2010 and cover multiple locations, not for only two data points in what are dry years and only at one gauge." In separate emails seen by the Herald, the Murray-Darling Basin Authority's acting general manager Peta-Joanne Derham has also privately backed the work conducted by Professor Sheldon.