Adelaide's Torrens lake in the city is high and dry because of a weir malfunction.
Adelaide City Council says the water level has dropped by more than two metres after the weir gate partially opened and had to be closed manually.
Water drained from the lake for about two hours.
The western end of the Torrens lake had already been closed because of an outbreak of blue-green algae.
The council says an electrical fault caused the malfunction.
It says the lake is unlikely to refill until enough rain falls in the River Torrens catchment zone, which takes in the Adelaide Hills.
South Australian Premier Mike Rann says the lake is an Adelaide tourist landmark and the loss of water is a big concern just weeks away from events including the Fringe festival and the V8 Supercar race.
"I'll get a report on that later on this morning to find out what happened and how it can be fixed," he said.
Adelaide Lord Mayor Michael Harbison says it would be irresponsible in ongoing drought to refill the Torrens immediately with water stored upstream at Kangaroo Creek reservoir in the Adelaide Hills.
The water mishap has exposed rusting shopping trolleys, lost skateboards and even a radio which was dropped by a rowing crew coach into the lake a few days ago.
The mayor of Charles Sturt Council in Adelaide's western suburbs, Harold Anderson, says the rush of water down the Torrens has left a mess downstream.
Garbage and millions of litres of dirty water have been flowing out to sea.
Mr Anderson is upset that he and council staff were not advised.
"When we've had the algae flushes over the years we've argued about it but, at the end of the day, being good councils between ourselves we don't do anything further about it except complain," he said.
"I'll be ringing the Lord Mayor a bit later on ... when I've settled down."
The president of the Western Adelaide Coastal Residents Association says the discharge from the Torrens lake into Saint Vincent Gulf is a disaster for the environment and for human health.
Jim Douglas says the water is turbid, high in nutrients and will aid the death of seagrass along the metropolitan coastline.
Mr Douglas says there is also an unknown level of danger for swimmers at Adelaide beaches.
"I think it's a disaster. That lake water also carries viruses and those viruses can actually hang around in that water for an unknown period of time," he said.
"Most of the bacteria and the viruses would be detrimental to human health."
Beaches have been closed for swimming north and south of the Torrens outlet, while Charles Sturt Council tests the water quality.
Pat Harbison from the Friends of Gulf St Vincent is also worried about the risk of environmental damage.
"If the water is very turbid or murky it stops the light from getting to the sea grasses and you know yourself the plants won't grow in the dark," she said.
"Not only that, at times the water along the coast is just not fit for swimming."http://www.abc.net.au/news/stories/2009/02/12/2489178.htm
Just for comparison, this is the Torrens normally:
And this is the Torrens now
Good ya, South Australia