The Windsor Essex County Health Unit has closed Holiday Beach in Amherstburg after testing revealed e.coli counts over 1,000 ppb.
The health unit tests the water at public beaches every Wednesday and releases the results on Fridays.
Warning signs are posted at four other public beaches in the region after they posted e.coli counts over 200 ppb.
Swimming is not recommended at Cedar Beach, Cedar Island Beach, Colchester Beach, and Seacliff Beach.
Sandpoint Beach in Windsor remains closed after the drowning death of a 15-year-old boy earlier this spring.