Dive Flag

A surface flag warning boats that divers are below: the red flag with a white diagonal stripe, or the blue-and-white international alpha flag.

A dive flag tells surface traffic that divers are in the water so boats keep clear and slow down. Two flags are in use worldwide. The diver down flag is red with a white diagonal stripe, flown from a boat, a float, or a buoy towed by the divers, and is the standard recreational flag in the United States and many other places. The alpha flag is a blue-and-white swallow-tailed signal flag from the International Code of Signals, flown by a vessel to declare that it has divers down and restricted ability to maneuver.

The practical difference is what each flag protects: the red-and-white flag marks the divers themselves, while the alpha flag is a legal statement about the vessel. Many boats fly both. Rules vary by country and even by state, covering how large the flag must be, how close divers must stay to it, and how far boats must keep away, commonly on the order of 15 to 90 m depending on jurisdiction.

As a diver, surface near your flag or your DSMB, especially in areas with boat traffic, and listen for engines before you come up. On drift dives the flag or float towed by the group is effectively your moving safe zone. Ascending well away from the flag, then making a long surface swim through open water, is exactly the exposure the flag exists to prevent.