RE: Rules and reulations for float flying in Massachusetts?
Local governments may have enacted "no fun allowed" regulations, but probably not, unless you see a sign posted.
Scope out the site. Spot physical hazards such as wires and trees. Take note of canoe rentals, beaches, other "no-fly" situations. Plan your flight area.
North-facing beaches are great. The sun stays out of your eyes.
Avoid irritating people. As at your club field, it is completely unacceptable to fly over anyone.
If you launch your plane while people are fishing in the vicinity it's just plain rude.
Most people are appreciative and curious. Engage them in conversation. Be a "Nice Guy". They'll be spectators and not complainers.
If somebody calls the cops, apologize and pack up your stuff immediately. Point out that you had looked and it's not posted, but are eager to obey regulations. Ask politely if other places are available where you might fly..
All that said, I have never been asked to leave a float-flying site. Floatplanes are cool to watch!