Indiana law requires that scuba divers or snorkelers display a diver-down flag to mark the diving area. The diver must stay within 100 feet of the flag. Vessels must stay at least 150 feet away from the flag unless directly involved in supporting the diver.
Two types of flags are used to indicate diving activity.
Divers Flag: A rectangular red flag, at least 12 x 12 inches in size, with a white diagonal stripe is used to indicate the presence of a submerged diver in the area. Indiana law requires that divers display this flag prominently and stay within 100 feet of the flag.
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 federal waters whenever these vessels are restricted in their ability to maneuver by the diving operation. 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.