Colac Otway Shire Council is advising people to avoid contact with Lake Colac water after water quality tests showed an elevated presence of enterococci levels.
Enterococci is used as an indicator of faecal contamination in water, and possibly the presence of disease-causing bacteria and viruses, which can sicken swimmers.
Eating fish or shellfish harvested from waters with faecal contamination can also result in illness.
Council chief executive Peter Brown said the expected source of poor water quality was stock, birds and dog faeces and that the council would begin a public awareness campaign encouraging people to clean up after their dogs.
But the council is yet to determine the source of contamination.
Mr Brown said the council had proactively tested the water at three sites at or near the lake in response to an increase in recreational use and was developing a management plan to monitor water quality and detect causes of poor water quality.
“There have been no reports of concerns but council will monitor the water quality to keep people informed if there are any issues,” Mr Brown said.
“Initial results of microbial testing at three locations along Lake Colac before Christmas indicated that further investigation was required to assess water quality in the lake and at Barongarook Creek.
“Tests recorded enterococci levels at Lake Colac beach at 88cfu/100ml and greater levels at Barongarook Creek and Armstrong Street stormwater outfall.”
A microbial result above 100cfu/100ml on a single sample is cause for further assessment.