The paper by Murray-Darling Basin Authority's (MDBA) own scientists found flow behaviour had changed since 2000, particularly in mid-sections of the river such as between the towns of Walgett and Brewarrina. On that section, low or no-flow periods were "difficult to reconcile with impacts purely caused by climate", the scientists said. Indeed, dry periods on the river downstream from Bourke were "significantly longer than pre-2000", with the dry spells during the millennium drought continuing afterwards. Water resource development – also described as "anthropogenic impact" – must also play "a critical role" in the low flows between Walgett and Brewarrina, the report said.

The Darling River is barely flowing south of Menindee Lakes. (The photo was taken on February 18 this year.) Credit:Katharine McBride 'Treachery' The revelations come after the Senate last month voted to disallow changes to the $13 billion Murray-Darling Basin Plan that would have cut annual environmental water savings by 70 billion litres. “The report is derived from data which belongs to the public, was prepared for public purpose by servants of the public using taxpayers' money, and should have been made available to the public," Rex Patrick, the Nick Xenophon Team senator, said, adding the information was "highly relevant to the Northern Basin Review debate". "That it wasn't made available for Parliament's consideration is nothing short of a treachery," Senator Patrick said.

A spokeswoman for the authority said the report was "undergoing quality assurance processes prior to publication", with a formal release on its website likely in coming days. Loading The MDBA commissioned the internal team to "address some of the specific concerns raised" by its own compliance reviews and those of the Berejiklian government, she said. Terry Korn, president of the Australian Floodplain Association, said the report confirmed what his group's members had known since the O'Farrell government changed the river's water-sharing plan in 2012 to allow irrigators to pump even during low-flow periods. Poor policy had been compounded by "totally inadequate monitoring and compliance systems", Mr Korn said.

"Some irrigators have capitalised on this poor management by the NSW government to such an extent that their removal of critical low flows has denied downstream landholders and communities their basic riparian rights to fresh clean water," he said. "This is totally unacceptable." Loading Sarah Hanson-Young, the Greens senator who led the recent disallowance to the proposed basin plan's changes, said the new report showed the MDBA had advised the Turnbull government "not to trust its modelling while telling the public everything is OK".The authority "has an enormous position of trust and this is exactly the kind of action that puts that trust at risk", Senator Hanson-Young said.“That's an enormous political intervention from an organisation that's already facing community concern over its failure to tackle endemic theft and corruption in upstream states."The report cited "a number of compelling signs indicating that river extraction is a significant (and possibly the leading) contributor" to the heavy reduction of some flow events.These included the fact they only occurred in specific reaches of the river, only after 2000, and often took place in pairs and at similar times of the year, it said. Sarah Hanson-Young, the Greens senator who led the recent disallowance to the proposed basin plan's changes, said the new report showed the MDBA had advised the Turnbull government "not to trust its modelling while telling the public everything is OK".The authority "has an enormous position of trust and this is exactly the kind of action that puts that trust at risk", Senator Hanson-Young said.“That's an enormous political intervention from an organisation that's already facing community concern over its failure to tackle endemic theft and corruption in upstream states."The report cited "a number of compelling signs indicating that river extraction is a significant (and possibly the leading) contributor" to the heavy reduction of some flow events.These included the fact they only occurred in specific reaches of the river, only after 2000, and often took place in pairs and at similar times of the year, it said. Niall Blair, the NSW regional water minister, said the government was "aware of this report" but detailed comments would be premature until it was finalised. "We have provided input to the MDBA to assist in the finalisation and publication of this work," he said.

"This kind of analysis assists the work of the NSW government in providing a robust and sophisticated compliance and enforcement approach in NSW rivers." A spokesman for David Littleproud said the federal Agriculture Minister's office had yet to receive the report.