Scuba divers and snorkelers must display a diver-down flag to mark their diving area. Divers must stay within a 150-foot radius of the flag. Vessel operators must stay at least 150 feet away from a diver-down flag and must exercise special care in the vicinity of a diver-down flag.
Scuba divers and snorkelers should not place a flag in an area already occupied by other boaters or where their diving operation will impede the normal flow of waterway traffic. Divers also should follow all of the water safety rules themselves.
Two types of flags are used to indicate diving activity.
Divers Flag: A rectangular red flag with a white diagonal stripe must be displayed on a vessel or flotation device while diving on state waters.
Alfa Flag: A blue-and-white International Code Flag A (or Alfa flag), at least 3.3 feet (one meter) high and visible from all directions, must be displayed on vessels on federally controlled waters. This flag indicates that the vessel is involved in a diving activity.