Let google be your friend......
Dive Flag Law
I would verify local laws, but this makes for a decent starting point.
"For Divers in Washington
Washington Dive Flags
Rules for WA divers and boaters
Washington specifies the use of the
alpha dive flag.
According to Adventures in Boating, Washington, The Legal Requirements of Boating:
Persons scuba diving, skin diving and snorkeling from a vessel must display an 'Alfa' flag to mark their diving area. Between sunset and sunrise, the flag should be lighted.
Divers should stay within 200 feet of the dive flag.
From WAC 296-37-535 Predive procedures for commercial diving operations:
When diving from surfaces other than vessels in areas capable of supporting marine traffic, a rigid replica of the international code flag "A" at least one meter in height shall be displayed at the dive location in a manner which allows all-round visibility, and shall be illuminated during night diving operations. "
Now how many of us are probably in violation of this one??? I for one know that I am. Most boaters don't know what a "Diver down" flag means when they see it, however, since everyone on the water (at least here in the US) falls under the Coast Guard Rules of the Road, then they should know what an Alpha flag means. I know from being in the Navy and being the one responsible for knowing Rules of the Road and training sailors on them, that most of my guys couldn't tell you what a diver down flag meant before I got certified, but everyone of them could tell you what an Alpha flag meant. Now everyone of them knows the diver down flag. Even diving this last weekend, the people on the dock were asking me, fully dressed and ready to get into the water, what the flag on the float that I had just put into the water meant. I politely informed them that it was to mark the area and to let nearby boaters know that there were divers in the water. Many were surprised to know that I was required to have the flag out.
Back to the original question. I dive with a diver down flag on a float every time I dive, with the exception of the Underwater Park across the sound from me. Only reason I don't take mine there is it is a designated Underwater Park, is marked with a diver down flag on a buoy on the far center of the park, and no boats/watercraft are allowed into that area.