Scuba divers and snorkelers must display a diver-down flag that marks their diving area. Vessels must remain at least 50 feet away from the flag unless the flag is located such that it creates an unreasonable obstruction to navigation.
Scuba divers and snorkelers should not place a flag in an area already occupied by other boaters or where their diving operations 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 inches by 15 inches, with a white diagonal stripe may be used if on North Carolina 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.