Divers and snorkelers should use a divers-down flag or buoy to alert boaters to the presence of people under the water’s surface.
Vessels must stay at least 100 feet away from a divers-down flag or buoy in a river, inlet or channel. In open water, including the Gulf of Mexico, vessels must stay 300 feet away. Divers should stay within the same distances of their displayed flag or buoy.
The divers-down symbol is rectangular or square and red with a white diagonal stripe. A divers-down flag displayed on a boat must be at least 20 inches by 24 inches and displayed at a high point where it can be observed from 360 degrees around the vessel.
A divers-down flag or buoy, displayed from the water, must be at least 12 inches by 12 inches. A flag must have a wire or something else to hold it open. A a buoy can be three- or four-sided.