Re: SCUBA in Boston Harbor
I am SCUBA certified, and actually did my checkout dives in Marblehead, it was in the late summer, and you really couldn't see anything. It was very cold, and it was something I probably wouldn't do again (Diving in mass, if I didn't have to). Diving in the Caribbean / florida on the other hand is awesome, and I am very glad I got certified so I can enjoy diving while on vacations.
What are you looking to do in boston harbor? I know some people dive and catch lobsters, I think you still need some sort of permit, I think there are also some wrecks people look at.
But you have to wear a thick wetsuit and a lot of lead weight to overcome the buoyancy of the wetsuit.