Scuba divers or snorkelers must display a diver-down flag that marks the diving area as required by the Texas Water Safety Act. Vessels must remain at least 50 feet away from the flag. If they have to approach the diving area, vessel operators must have permission from the person who placed the flag or the vessel displaying the flag. Outside of 50 feet, vessel operators must operate at "headway speed" out to a distance of 150 feet away from the flag. Patrol or rescue craft are exempt from such requirements.
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, at least 15 x 15 inches, with a white diagonal stripe is required on state waters.
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 federally controlled waters. This flag indicates that the vessel is involved in a diving activity.