Federal law requires that scuba divers or snorkelers on federally controlled waters display the Alfa diver-down flag to mark their diving area. Two types of flags are used to indicate diving activity.
A rectangular red flag, at least 15 x 15 inches, with a white diagonal stripe is used to indicate the presence of a submerged diver in the area. Display of this flag is not required by Oregon law and does not in itself restrict the use of the water; however, boaters should always use caution and slow to “slow, no wake speed” (maximum 5 mph) when operating within 200 feet of a displayed flag.
Alfa Flag (federal)
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 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.