Namoi Water chief executive, John Clements, who represents water users in the Namoi catchment, said federal funds promised for water buybacks should be used to buy out farmers at the bottom of the Murray and open the barrages to sea water.

"These guys down there are trying to live in a world that cannot be sustained," he said.

"What are you going to do? Are you going to push good water from the northern system down a dry river and then put this fresh water into a saline system and watch a lot of it evaporate? No, you should just tell them this 1930s experiment is over."

He said Murray-Darling Basin Commission figures estimating that 750 to 950 gigalitres of water evaporate each year from Lakes Albert and Alexandrina showed it was folly to attempt to maintain the shallow lakes as fresh water systems.

His comments came as the Greens and Independent Senator, Nick Xenophon, called for an urgent inquiry into how to save the lower lakes and the Coorong at the Murray mouth as fresh water ecosystems.

The federal Coalition has flagged its support package for communities around the lower Murray. Mr Clements' comments have triggered an angry backlash in South Australia.

Former South Australian Liberal Premier, Dean Brown, who advises the current State government on drought policy, said the region was a major agricultural producer and that important ecosystems would be lost if the barrages were opened to sea water.

"Some of these people fail to appreciate that if you have a river system that has a salt load in it and you build a barrier part-way up the river and let the seawater in, you just shift the problem further and further upstream," he said.

"I think the people who come up with these suggestions about closing it off and turning it into seawater do not even start to comprehend the river system and the magnitude of the industry."