Diver-down flags are used to indicate divers or snorkelers in the immediate area. When operating in an area where one of these flags is displayed, vessel operators should exercise caution.
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, at least 15 x 15 inches, with a white diagonal stripe, flown from a vessel or a buoy.
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.