Dive Flag Law
Rules for U.S. divers and boaters
The U.S. Coast Guard spells out the federal regulation for dive flag use in Rule 27e - Vessel Engaged in Diving Operations:
Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in paragraph (d) of this Rule [most civilian vessels], the following shall be exhibited:
Three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white; a rigid replica of the International Code flag "A" not less than 1 meter in height. Measures shall be taken to ensure its all-round visibility.
Click here for more on the "A" flag or alpha flag.
In Canada, boating is a federal responsibility so there is one standard for the whole country. See this page on Canadian dive flag law.
The U.S. federal government has no rules about using the red-and-white dive flag. However, most U.S. states do, and so do some local governments.
There is no consistent, simple rule in the U.S. It often depends on where you are, how far off-shore you are, and whether you're diving from a boat. Moreover, it's often not easy to find the law that applies to you. Generally, the first place to look is in the rules governing boating, often published by the state department of natural resources.
The following is a compilation of the rules for each U.S. state. There is no guarantee this is comprehensive or up-to-date. You should check with local authorities.
A special thank-you goes out to Julie Richardson from DiveWise, a "freediving education initiative." She generously helped fill-in the pieces that were missing from our collection. If you see other missing pieces, or have updates or information that would be useful, please contact me at chris-(@)-interesting.com (remove the hyphens and parentheses). I'd appreciate your help.
By the way, there is another flag that's sometimes used in diving operations, in addition to the red-and-white dive flag and the blue-and-white alpha flag. It's the "P" or "papa" flag.
The papa flag is a blue rectangle with a smaller white rectangle inside it. It's used to signal "all personnel return to ship" and is often used to recall divers.
chris-(@)-interesting.com (remove the hyphens and parentheses)
P.S. This information was as complete and up-to-date as I could reasonably make it. This material is not a complete analysis of the topic and should not be construed as providing legal advice. Readers should conduct their own appropriate legal research or contact an attorney in their own state.