INDEPENDENT senator Nick Xenophon says he will work with the South Australian government on a possible High Court challenge to the draft Murray-Darling Basin plan.

Premier Jay Weatherill has not ruled out taking the issue to the High Court, describing the proposals as inadequate.

Senator Xenophon is equally angered and says South Australia is facing the "fight of its life" to get a fair go.

He said the plan would rob water from SA and did not acknowledge the water efficiency measures already employed by local irrigators.

A High Court challenge could proceed on the basis that the basin plan did not meet Australia's international environmental obligations or in relation to the trade in water between states.

"I would welcome working with the South Australian government, with Premier Jay Weatherill in relation to that," Senator Xenophon said.

"We need to get this right because doing nothing is not an option."

The Murray Darling Basin Authority's draft Basin Plan released today is set to have a major impact on local irrigators, who have long capped water extraction.

It could slash the take of water in SA's stretch of the Murray by more than 25 per cent - despite pleas from the State Government for no cuts in recognition of the savings already made. Under the plan, 2750 gigalitres a year will be restored to the system to keep it flowing - more than a thousand gigalitres less than the 4000GL experts say is needed.

The water won't have to be fully restored until 2019, and will be reviewed in 2015.

Much of that water has already been secured through buybacks, leaving about 1468GL to recover over the next seven years.

In SA, the Murray allocation could be cut by as much as 180GL - water worth more than $300 million. Up to 101GL will be cut from the 665GL diversion limit, with 79GL already secured. But another 971GL will also need to be recovered from across the southern basin, and it is estimated SA's share could be as much as 80GL.

The plan warns the Riverland - struggling from the decade-long drought - will be especially vulnerable with less water available, and the impact will flow on to the whole community.

"While irrigators will be paid for water they choose to sell, the consequent reduction in irrigated production may trigger third-party flow-on effects among those farmers who remain, businesses that service farmers, processing companies, and community level businesses and services," the plan says.

Premier Jay Weatherill, who threatened that the state would pursue legal action if the plan returned less than 4000GL to the system, is urging South Australians to show a unified front to call for a better deal for the state.

"This is going to require all of the resources that we can muster, " he said.

"All of those distinctions - the city, the country, the environmentalists, the upper reaches and the lower reaches, I think we've got to set them aside.

"There's one fundamental truth. That is that the more water we have in the river, the healthier the river is."

Water Minister Tony Burke, who travels to Adelaide this week, argued the new plan was a "once-in-a-generation opportunity".

"Murray-Darling Basin reform has been put in the too-hard basket for too long and for too long the process of returning our rivers to health has been caught in a deadlock between the states," he said.

"The Gillard Government will not wait until the next drought to act. I'm not prepared to stand idly by while the system enters the next drought already in a poor state of health."

SA Liberal senator Simon Birmingham said SA had been "dudded".

"South Australia appears to have copped a double whammy in this plan, with less environmental water and potentially bigger cuts to our irrigators than was proposed a year ago," he said.

"It would seem that SA is worse off under this latest plan than we were under the earlier version. SA looks likely to be asked to provide higher cuts towards a lower national total. Many South Australians will feel justifiably dudded."

Australian Conservation Foundation campaigner Dr Paul Sinclair said "2750GL fails the river, fails regional communities and fails the national interest".

"We need to have an independent assessment of how the authority reached this decision," he said.

The new plan comes more than a year after the authority's doomed draft blueprint to save the river was released.

That draft recommended 3000-7600GL was needed to restore the system.

That prompted a backlash from irrigators and the authority withdrew the plan just days later.

Former NSW water minister Craig Knowles was appointed the chairman of the authority in January, with his task to come up with a new version of the rescue plan.

His version is based on new scientific modelling and has recommended less water is needed to restore the system.

The plan has been released for a 20-week consultation period, with fiery meetings expected across the basin.

Fourth-generation fisherman Henry Jones from Clayton Bay is a member of the Basin Community Committee advising the authority.

He says people in the eastern states refuse to accept responsibility for the river. "I don't believe it's enough for South Australia. However I can see if it's too much the eastern states are just going to walk away," he said.