dead fish
© Glenn MilneJohn Ross, 5, checks out a dead cod in the Murray River near Wemen.
Ten billion litres of environmental water will be released into the lower Goulburn River in a bid to clean up the river and protect native fish, the Department of Sustainability and Environment said yesterday.

But locals say the move is too little too late. People at Mildura and Robinvale are reporting fish up to 1m floating belly up down the river and crayfish climbing up river banks to breathe.

Jodie Ross, who runs the general store in Wemen, southeast of Mildura, said the black water started in Swan Hill and reached Wemen on New Year's Day. She said the dying fish were a devastating sight for river communities.

"We are seeing hundreds of dead fish floating by and even the live ones are coming up to the top as though they are very weak," she said.

Ms Ross said the river bank was lined with dead shrimp and yabbies.

"Crayfish are normally buried deep in the mud this time of year and they are climbing up the bank because they can't breathe; they are baking on banks of the river," she said.

Mark Bailey, of Goulburn Murray River Water, said the black water was caused by the rapid decay of leaves and twigs accumulated during floods. The decay caused low oxygen levels in the water and suffocated fish and other aquatic life.

The Murray Darling Basin Authority released fresh water from irrigation systems and environmental water from storages before Christmas in an attempt to dilute the black water. NSW authorities are also carrying out an emergency fish rescue in a bid to move native fish.

But Ms Ross said authorities had acted too late. "The black water has wiped out the Murray River, all the fish are dead," she said.

Mr Bailey said the river would begin to rejuvenate within weeks. But Ms Ross said the effects would be felt for years.