According to River, Lakes and Coorong Action Group member Di Bell, the visitors were there to grieve.

“Watching, on a daily basis as thousands of tonnes of clay and sand and rumble are being dumped in the channel between Hindmarsh Island and Clayton Bay, hearing the whine of the trucks and knowing that this weir will cut Lake Alexandrina off from the fresh water of the Finniss River and Currency Creek has been painful," she said.

"A complex eco-system is being cut into pieces and there are no credible plans to undo the damage.”

Senator Sarah Hanson-Young, who was in attendance with her daughter, said building a regulator at Clayton Bay was "ecological vandalism".

Overlooking the construction of the weir, the "mourners" processed to the water’s edge where they poured water from the tributaries into the narrow stretch of water still running between the cliff and the weir wall.

Ms Bell said the "tragedy of this engineering intervention in the life of the river is that there is no good reason to build it," she said.

"Our most recent monitoring shows that the water coming down the Finniss River and Currency Creek is not acidic. The rains have diluted the acids and the water at the weir site is alkaline. The country is greening up. A prudent policy of a responsible government would be to ensure that fresh water from the tributaries continues to flow and is not dammed and diverted further upstream.”

Adelaide University's Dr Mike Geddes spoke in support of RLCAG’s position on the acid sulfate soils issue.

“It has been over-stated and dominated the debate," he said.

"It is based on sound analysis of soil chemistry but little understanding of the implication for water quality and the ecology of the system. In my view this great earthen wall represents the biggest environmental insult to the River Murray system.”

The Fresh Water Embassy at Clayton Bay has been open every day and will stay open for the duration of the construction.

* Details: www.hurrysavethemurray.com