Walkers Lake near St Arnaud was temporarily closed after water testing confirmed the presence of blue-green algae in the waters.
The algae could cause rashes, sore eyes, ears and nose and severe vomiting and nausea when swallowed.
Northern Grampians Shire Council mayor Tony Driscoll said the lake was a health risk and must be avoided.
“We understand this is disappointing for the many frequent users of Walkers Lake, as well as tourists visiting the area at this popular time of year,” he said.
“Health and safety must be our number one priority and for that reason, the lake will be closed until we can confirm that it is safe for use.”
Cr Driscoll said it was crucial people did not come into contact with the water.
”This includes swimming, drinking, boating, and fishing,” he said.
Town pet owners were also advised to keep their pets away from the lake.
Council erected signage at the lake and will undertake another water test in three weeks in line with expert advice to determine if the lake could be opened.
Ararat’s Alexandra Lake was also declared a health risk after blue-green algae was found in its waters.
The lake was also closed until further tests could reveal the toxic bloom had completely cleared.
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