The 5,000-strong crowd gathered near the mouth of the 2,530 kilometre (1,569 mile) Murray to hold two minute's silence to mark the 'death' of the river, which forms part of Australia's most important agricultural region.

Kym McHugh, mayor of the local Alexandrina Council, said the ceremony near the South Australian town of Goolwa was to "underscore this eleventh hour bid to save the nation's greatest river."

"It sent a very clear message by saying we've had a lot of talk about the river system, a lot of science, we all know what the problem is -- we just want politicians to have the will to fix it up," he told national news agency AAP.

"They need to secure water upstream and send it down."

Water levels are so low in the Murray River, due to drought and irrigation, that the freshwater lakes the river feeds into are turning to acid.

The federal government last week said there was not enough water in the system to save the freshwater lakes, leading to suggestions that ocean water could be used to prevent the lakes from drying out.

But the council wants the government to release water held in storage in upstream states into the river so it can flow down and prevent an environmental, economic and social disaster in the region.

"We need to give these lakes another chance," McHugh said.

The Murray, along with the 2,740-kilometre Darling River and 1,690-kilometre Murrumbidgee River, form the Murray Darling Basin, which accounts for some 40 percent of the nation's agricultural production.

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