The Turnbull Government and the Murray Darling Basin Authority have questions to answer, Greens water spokesperson Senator Sarah Hanson-Young has said.
"Today's leaked report shows the MDBA advising the Government not to trust its modelling, while telling the public to do exactly that.
"This report puts the blame for the ailing health of the Darling on man-made water extraction, at a time when the Senate is being asked to approve even more water being taken out of the system.
"The Murray Darling Basin Authority enjoys an enormous degree of public trust and this is exactly the kind of action that puts that trust at risk.
"This sort of behaviour is typical from Barnaby Joyce and the man he installed as the latest water minister, but we should expect better from the MDBA.
"The fact they've had this report for three months and they've sat on it represents an enormous political intervention from an organisation already facing community backlash over its failure to tackle endemic theft and corruption in upstream states.
"And the fact it's leaked today shows that some within the organisation, or within the government, have concerns with the extent to which the MDBA's placed its 'independent' thumb on the scales.
"it's vital that the Murray Darling Basin Plan is independently audited and that the public is made aware of what is really going on within the Murray Darling Basin Authority."