The Walpole Island Health Centre warned people not to swim in the Willow Beach area on Monday.
The Walpole Island First Nation Council shared the advisory on its Facebook page.
The health centre said the recommendation is to not swim when e-coli counts are in excess of 100.
"The count in this area is 130 for e-coli and is in exceedance. It is not recommended to swim in this area as there is increased risk to eye, ear, throat and gastrointestinal illness," the notice read.
The health centre says Walpole Island's other beaches are clear for swimming.
