Grey Bruce Public Health has declared the Southampton Beach unsafe for swimming.
This comes after recent water-sampling results showed bacterial levels exceeding Ontario Ministry of Health standards.
The beach posting will remain in effect until further samples show levels have returned to within the acceptable range for swimming and bathing.
Residents and visitors to the area are reminded that swimming or playing in water with bacterial levels above provincial standards for bathing can increase the risk of skin, eye, ear, nose, and throat infections or gastrointestinal illness.
Pet owners should keep pets away from the water and refrain from letting pets drink it, too.
"While we understand that this posting will be an inconvenience to some, we respectfully ask that residents and visitors respect this swim advisory as people are at an increased risk of getting sick or an infection when bacterial levels in beach water exceed Ontario guidelines" said Senior Public Health Manager, Andrew Barton.