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.
Two types of flags are used to indicate diving activity.
A rectangular red flag, at least 14 x 16 inches, with a white diagonal stripe that is one-fifth the width of the flag must be mounted on a float or buoy. For boats tending free-swimming divers where the diving does not interfere with the maneuverability of the vessel, the divers flag may be displayed.
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. The Alfa flag should be used by vessels engaged in diving operations and restricted in their ability to maneuver.
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.