THE Yarrowee River was contaminated with sewage when a sewer main overflowed and spilled into the water body recently.
Central Highlands Water spent several days cleaning and pumping the Yarrowee River last week after receiving reports of a sewage smell near Hill Street, Ballarat.
The river has since been decontaminated and is currently being monitored.
Central Highlands Water said a construction material had blocked a sewer main upstream of Hill Street.
"On Sunday, May 18, CHW received a call reporting a possible sewer smell from the Yarrowee River," a CHW spokesperson said.
"A full investigation was conducted by CHW and it was found there was a foreign object upstream ... some 3.5 kilometres away in Duncan Street, which caused a sewer main blockage.
"The blockage was cleared and the affected area of the creek was tidied up."
He said signs had been erected along the walking path to notify the public of the contamination.
"It's a rare situation, you can get people putting all sorts of things down the pipes," he said.
The Courier was contacted by a resident who saw dead fish next to the river.
CHW confirmed they removed some dead fish.