The Florida Department of Health in Pinellas County is warning swimmers to stay out of the water at Fort De Soto Park's north beach because fecal pollution has been detected there.
The pollution can come from stormwater runoff, pets, wildlife and sewage, and can cause people diseases, infections or rashes, a written statement said.
"This area should be considered a potential health risk to swimmers," the agency said.
The warning could stifle or change plans for residents and tourists who typically flock to the park every weekend. The next water sampling will take place on Monday.
The agency conducts the testing through the Healthy Beaches Monitoring Program.