Murray-Darling Basin 450GL environmental water stuck without easing constraints

The federal government's latest move to create a Murray-Darling Basin agreement without Victoria, the key state that delivers water to South Australia, has raised more concerns the whole proposal is divorced from reality and a political box ticking exercise.

Labor has promised to recover an additional 450GL for the environment, but the extra water is physically unable to move around the system without easing several bottlenecks, called 'constraints'.

The basin state governments are working on several projects to ease constraints, but many are over budget and behind schedule.

A new agreement with the Commonweath will provide the states with more time and money to complete the projects. However Victoria has suspended its constraints projects and is holding out from the new agreement.

Without Victoria completing its projects, the environmental water will not get to South Australia, regardless of how much water is recovered or bought back.

Federal Water Minister Tanya Plibersek says the idea that additional water couldn't be moved around the system without addressing constraints was "just wrong".

Her office later clarified that without the completed constraints projects, the environmental water can still flow down the Murray, however Victoria would not get the floodplain benefits.

NSW Irrigators' Council chief executive was concerned by the Water Minister's comments, which suggested the whole affair would be a box ticking exercise, and the government would buy environmental water without an environmental outcome.

"Tanya Plibersek can buy as much water as she wants from the Goulburn River, she won't be able to get it into the Murray in South Australia without fixing constraints," she said.

"[Without fixing constraints] they'll basically use the Murray as a big drain. Running the river that high for a long time is really bad for the environment, it creates erosion and bank destabilisation."

The Murray-Darling Basin is highly regulated and designed to prevent floods, which means many habitats miss out on the small-to-medium floods they evolved around, such as the Chowilla floodplain above the SA Riverlands.

To ease constraints and allow controlled flooding that doesn't destroy towns and farms, state governments must negotiate around 6000 voluntary flooding easement agreements with landholders. Other constraints projects include physical barriers such as raising bridges and altering roads.

As the Murray runs along the NSW-Victorian border, the constraints projects have been designed as a joint project between the two state governments and will not be completed unless agreements are struck with all landholders on both sides of the river.

The Murray Darling Basin Authority was asked if it had modelled how the additional additional 450GL will be moved around the system if the constraints projects are not completed.

"Work informing the Basin Plan at the time it was agreed in 2012 looked at the environmental outcomes that could be achieved from returning the 450 gigalitres with and without easing constraints," MDBA science acquisition general manager Dr Matt Coleman said.

"Easing constraints will enhance environmental outcomes, as they enable the rivers to connect to the floodplains and wetlands more easily."

It's understood Victoria is still discussing the new agreement with the Albanese government, but is concerned the Commonwealth is focused on numbers on a page rather than environmental outcomes.

"The door is still open to the Victorian government, we would certainly like to see them sign up as other states and territories in the basin have done," Ms Plibersek said.

Labor's new basin proposal will be put under the microscope of a Senate inquiry before being voted on. The government hopes to have it passed by the end of the year, however will have to convince the Greens, who will turn down the bill unless it includes an iron-clad guarantee the 450GL will be recovered.