Persons scuba diving, skin diving, or snorkeling must display a red-and-white divers flag. Divers or snorkelers must remain within 100 feet of the divers flag. If possible, vessel operators not engaged in the diving operation must stay at least 100 feet from a displayed flag. If not possible, vessel operators must reduce speed to no more than three miles per hour.
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 with a white diagonal stripe, at least 12 x 15 inches in size and constructed of rigidly supported material, must be displayed on a vessel or surface float and must extend a minimum distance of three feet up from the surface of the water.
Alfa Flag: A blue-and-white International Code Flag A (or Alfa flag) must be flown from a vessel restricted in its ability to maneuver. This flag indicates that the vessel is involved in a diving activity. The Alfa flag may be displayed in addition to the divers flag but does not replace the divers flag.