Scuba divers or snorkelers must display a diver-down flag to mark their diving area. Bubbles also may indicate that a diver is below. Vessels must maintain a distance of at least 25 yards from any displayed 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: The red-and-white divers flag is used on state waters and must be at least 12 inches by 12 inches.
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.