Health advisories have been posted for Jupiter Beach Park, Riviera Beach, Phil Foster Park and Midtown Beach in Palm Beach.
Bacterial levels in the water placed the water quality in the poor range, according to the Palm Beach County Health Department.
Wildlife, heavy recreational use, high surf from high winds and high tides or runoff following heavy rains can cause the problem, the Health Department said.
Palm Beach said it has closed Midtown Beach to swimming and "is working to have the water quality resampled" so the beach can reopen as soon as possible.