The Windsor-Essex County Health Unit has closed one beach and posted five others as unsafe for swimming.
The public health agency is out with its weekly beach testing results and says Holiday Beach is closed because of high counts of e-coli in the water.
Cedar Beach, Cedar Island Beach, Colchester Beach, Lakeshore Lakeview Park West Beach and Seacliff Beach in Leamington have elevated levels of e-coli and are unsafe for swimming.
Point Pelee North West Beach is open.
The Health Unit adds blue green algae has not been observed in the water at any of the beaches.