Bird Key/Ringling Causeway is among three sites still testing beyond safe limits for enterococcus bacteria, the Florida Department of Health said.
The Sunday morning event is expected to host about 200 athletes in a variety of events.
The service has been in operation since 2017.
Mini reefs and oyster gardens are intended to attract the kind of marine life that will naturally cleanse the water.
County commissioners OK extra stop signs in Siesta Village.
