A $1.8 billion fund set up to boost environmental water flows in the Murray Darling Basin will broadly fail, after the Morrison government killed off a scheme to recover water from farmers.
An independent review has found the federally funded Water for the Environment Special Account (WESA) won't achieve either of its goals.
The basin will not receive the 450 gigalitres of extra water promised for the environment by June 2024.
And a large body of work to dismantle or modify constraints - often physical barriers that prevent natural water flows - will not be completed by then.
That is despite a total of $1.775 billion having been set aside since 2014, most of which has not been spent.
The review followed a 2021 decision by then water minister Keith Pitt to axe the $1.5 billion Water Efficiency Program that helped irrigators fund water infrastructure improvements.
Water savings from work such as lining irrigation channels were then split between the irrigator and the environment but Mr Pitt dumped the scheme, saying rural communities could not sustain the economic hit from reduced irrigation.
He said the 450 GL would be recovered from other "off-farm" sources, such as upgrading water pipelines, but the review released on Tuesday says that won't happen.
"It is not possible to reach the 450 GL target through the current efficiency measures program - the Off Farm Efficiency Program - even if the WESA's time and budget limits were removed," it found.
"Putting aside program and timing limitations, the estimated cost to recover the full 450 GL through efficiency measures is between $3.4 billion and $10.8 billion."
Only 2.6 GL has been recovered or contracted to be recovered through previous efficiency programs but the review noted it was possible to recover up to 60 GL more under the off-farm scheme by June 2024.
On efforts to deal with constraints to water flows, it found only two of six projects "could possibly be delivered by June 30, 2024, but it is not possible for the other four projects to be implemented by this date".
Environment and Water Minister Tanya Plibersek said the failure had nothing to do with a lack of money.
"It was a lack of will. It shows nine years of inaction on the 450 GL, with a fund just sitting there."
The Conservation Council of South Australia says the review is a depressing summary of what years of poor decision-making can do.
"The previous government decided to step away from cheaper options and only do the off-farm efficiency approach, which is a hyper-expensive way of returning water to the system," chief executive Craig Wilkins said.
"If we were to try to secure the full 450 GL using the previous government's preferred methodology the potential expense is more than $10 billion."
Mr Wilkins urged Ms Plibersek to make sure what is left in the fund is used for voluntary water buy backs, a position backed by the Greens who have accused the Coalition of funnelling billions of dollars into "bogus projects".
"My message to Minister Plibersek is: go and buy the water. Anything short of the 450 GL is unacceptable," said the party's water spokesperson Sarah Hanson-Young.
The opposition's water spokesperson said the review had a narrow focus on just one part of the basin rescue plan.
Deputy Nationals leader Perin Davey said the report highlighted the importance of cooperation from all states with a stake in the health of the basin.
The NSW and Victorian governments had repeatedly warned that recovering an additional 450 GL would have major social and economic impacts and would fuel environmental degradation if constraints weren't addressed, he said.
"This WESA report shows that we, in government, were willing to adjust and adapt to maximise the outcomes being achieved environmentally, socially and economically."