NH Regulations

Diving

NH Rev Stat § 270:31
I. Any person engaged in scuba diving on any of the public waters of the state and any person engaged in snorkeling in normally traveled navigable public waters shall have a diver's flag, consisting of a red flag with a diagonal white stripe, displayed indicating that diving activities are in progress. The bottom of said flag shall extend at least 3 feet above the surface of the water, the view of which shall be unobstructed for 360 degrees. 
II. Any person engaged in scuba diving or snorkeling shall remain within 75 feet of their dive flag.

Lobstering

If you don't know the rules, you could end up losing your dive gear. We are going to help you avoid that.

The New Hampshire senate rejected a bill in 2022 that would allow scuba divers to recreationally harvest lobsters. 
https://www.nhpr.org/nh-news/2022-04-29/nh-senate-rejects-lobster-licenses-for-recreational-scuba-divers

Boating around Divers

NH Rev Stat § 270:31
II. Boaters shall remain a minimum of 150 feet away from any posted dive flag, unless there are circumstances which prevent the operator from maintaining a minimum of 150 feet, in which case the operator shall maintain headway speed.