The Windsor-Essex County Health Unit warns that three local beaches are not recommended for swimming this week.
Bacteria levels are too high at Mettawas Beach in Kingsville, Sandpoint Beach in Windsor, and West Belle River Beach in Lakeshore.
E. coli counts are between 637 and 915.
Holiday Beach in Amherstburg remains closed because erosion from high water levels on Lake Erie has made it unsafe.
Warnings are posted when the water samples have E. coli levels that are greater than 200 per 100 millilitres of water and are shut down when the E. coli count is 1,000 per 100 millilitres of water or higher.
People can get sick from water with high levels of E. coli. The most common illnesses are stomach and intestinal illnesses such as vomiting and diarrhea, along with lung, eye, ear, nose, or throat infections or skin issues. Swallowing contaminated water is the main way people may get sick.
Health officials have started conducting beach water quality monitoring at all nine public beaches at least once a week. The testing runs from June to September to make sure the E. coli counts in the water are below provincial standards. Beach sampling will take place every Monday and if the beach is closed due to high E. coli levels, it will be resampled on Thursday of the same week. Beach water quality results are released every Wednesday during the summer.
The health unit does not recommend swimming after a heavy rainfall even if the beach is open for swimming.