Delays in critical state-led projects, along with climate change and shortfalls in water recovery, are putting the Murray-Darling Basin Plan under pressure.
Marking a decade since the creation of the blueprint for managing Australia's largest and most complex river system, its newest overseer, Andrew McConville, outlined its future to the National Press Club on Tuesday.
Armed with a report examining how the states are progressing on delivering 605 gigalitres of Murray Darling water back to the environment, he predicted some won't be delivered on time.
Some 36 projects are supposed to be complete by June 2024 but the Murray-Darling Basin Authority expects six will not meet the deadline.
They include one at Menindee Lakes in far western NSW, where the state government is attempting to reduce evaporation.
"Much has been achieved but there's still much to do ... we expect a shortfall of between 190 and 315 gigalitres," Mr McConville told his audience.
"This means the authority will have no choice but to recommend to the federal water minister amended sustainable diversion limits in southern basin catchments."
So far about 2,100 gigalitres or four Sydney Harbours-worth of a planned 2,680 gigalitres had been returned to the environment and state-led initiatives were meant to make up the difference.
The basin authority boss ramped up the pressure on government to remain committed.
"Governments must work hard and they must stay the course," he said.
"Has enough water been recovered to sustain the Murray-Darling Basin? And are our rivers set up to deliver the water that has been returned to the environment?
Mr McConville said water management was the most complex thing he's had to get his head around.
Appointed to his post four months ago, he said consideration needed to be given to climate change and Indigenous water management practices when reviewing the plan.
CSIRO modelling had shown river flows could fall 30 per cent by 2050 due to changing weather patterns.
"Is the basin plan adapting in the right way to climate change? If so, what are the implications of that? That could be part of that report that we'll put to the minister," he said.
Moreover, First Nations people needed to be involved in the solution.
"We need to rethink how do we incorporate Indigenous knowledge into the way we manage water," Mr McConville said.
"Turning around the decline of the health in our rivers and wetlands and flood plains takes time, it doesn't happen overnight."
The Murray-Darling Basin Plan will be reviewed in 2026.