Scuba divers or snorkelers must display a diver-down flag that marks their diving area. The person(s) diving must stay within 100 feet of the vertical position of their diver-down flag. Vessels must remain at least 200 feet away from a 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, at least 14 inches x 16 inches with a 3½-inch white diagonal stripe, must be displayed if on Michigan 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.