Persons scuba diving, skin diving, or snorkeling must display a red-and-white divers flag at or near the point of submergence that is capable of being identified from at least 100 yards. Divers or snorkelers must stay within 100 feet of their flag. Vessels not engaged in diving operations must stay at least 100 feet away from a 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: A rectangular red flag with a white diagonal stripe must be attached to a vessel, float, or buoy if on Colorado 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.