Scuba divers or snorkelers should display a diver-down flag that marks their diving area. Vessels must reduce speed to “no wake speed” while within 100 feet of the 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 indicate diving activity.
Divers Flag: A rectangular red flag with a white diagonal stripe is used on 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.