The Bendigo city council's advising dog owners around the city not to allow their pets into the water at Harcourt Park in Strathdale after a Blue Green algae bloom was discovered earlier this month.
The off lead park on Crook St is a popular spot for dog owners to meet and greet and signs have been put in place to warn locals of the dangers posed.
The algae is known to cause nausea, disorientation and itchy skin if ingested by animals and owners are advised to seek veterinary advice if their pets show symptoms.
Council's safe and healthy environments manager Caroline Grylls says people should be vigilant if they go to the park.
"I'd still encourage owners to bring their dogs along and continue to socialise them at the park but it will be up to individual owners to determine if they want to go there while the bloom is still there," Grylls said.
Lake Eppalock, Cairn Curran reservoir and Lake Joanna in Castlemaine have also been infected by the algae in recent weeks with blooms lasting anywhere from a couple of weeks to a couple of months.