Types of Diver-Down Flags
Two types of flags are used to indicate diving activity.
A rectangular red flag with a white diagonal stripe, at least 15 x 15 inches in size, is used if on New York state waters. The flag should be attached to a float.
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.
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.