Scuba divers or snorkelers may display a diver-down flag to mark their diving area. Vessel operators must not operate at greater than “no wake speed” within 100 feet of a displayed diver-down flag. Divers must stay within 100 feet of a displayed diver-down flag while at or near the surface. A diver-down flag may be displayed only while diving operations are underway.
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 should also 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 12 x 12 inches, with a white diagonal stripe may be displayed on the vessel or a buoy and must be displayed at least three feet above the surface of the water.
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.