Swim advisories have been issued for beaches 2 to 5 at Innisfil Beach Park, after a high level of bacteria was found in the water.
The Simcoe Muskoka District Health Unit (SMDHU) issued the advisory on Thursday.
A swimming advisory is issued when bacteria levels exceed those considered acceptable by the SMDHU.
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According to the advisory, elevated bacteria levels may increase the risk of developing minor skin, eye, ear, nose and throat infections, as well as stomach disorders.
While an advisory is not a beach closure, the town recommends that those who choose to swim during an advisory avoid ducking or dunking their head underwater.