Hundreds of billions of litres of water that should have flowed back into the Murray-Darling Basin is missing, according to a new report.
A report from the Australian National University has accused the government of grossly exaggerating the amount of water being returned to the Murray-Darling Basin.
More water than all of Sydney Harbour is missing from the Murray Darling Basin - equating to hundreds of billions of litres of water - according to the new research released on Wednesday by ANU's professors Quentin Grafton and John Williams.
"The sort of volumes we're talking about here, we're estimating it's 630 gigalitres less than what the government says," Professor Grafton told SBS News.
The Murray-Darling Basin Plan aims to remove water from irrigated agriculture, and return it to the river system, as well as buying back water from irrigators.
But the new research claims the government has grossly exaggerated the amount of water being returned to the Basin at all and Professor Grafton suggests it is contributing to ecological issues affecting the river.
"Either way you cut and slice this, this is a large amount of water and not having that amount of water is going to cause the crises that we currently have in 2019, and in years to come," he said.
But the report's critics believe those numbers just aren't possible.
"Unfortunately you can't estimate that based on a single mathematical model, which doesn't actually take into account that there are lot of different styles of recovery that have been embarked on," National Irrigators Council's CEO Steve Whan said.
The Government estimates that around 700 gigalitres of water has been recovered and NSW Water Resources Minister David Littleproud said this claim is supported by a University of Melbourne study released in October last year.
"It is unarguable that 700 gigalitres in water entitlements, previously held by irrigators , is now held by the Commonwealth Environmental Water Holder," he said in a statement.
Professors Williams and Grafton were both offered the chance to participate in that study, but declined.
The recent Royal Commission recommended sweeping changes to the Murray-Darling Basin Plan, including reallocating more water from irrigation to the environment.