Scuba divers or snorkelers must display a diver-down flag that marks their diving area. The flag must be displayed whenever someone is diving below the surface. Vessels should stay as far away from a diver-down flag as is reasonable and prudent for the circumstances. The suggested safe distance is 100 yards.
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: The diver-down flag that is recognized and used on Arizona waters, including the Colorado River and Lake System, is a rectangular red flag with a white diagonal stripe.
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.