Types of Diver-Down Flags
Two types of flags are used to indicate diving activity.
A rectangular red flag with a white diagonal stripe is attached to a vessel, float, or buoy.
A blue and white International Code Flag A (or Alfa flag), at least 3.3 feet (one meter) high and visible from all directions, is flown from a vessel on federally controlled or international waters that is restricted in its ability to maneuver. This flag indicates that the vessel is involved in a diving activity.