Acadia National ParkIs Located near the town of Bar Harbor. This spot has been officially recognized as clothing optional for many years, going back to the 1940's. Park officials allow nudity there, and do not bother sunbathers as long as they follow these rules:
No lewd behavior or sex.
The nude sunbathing area is on an outcrop of rock ledges on the east edge of the lake, hidden from any public area, and provides great diving and swimming.
Follow the trail through the woods and decend to the clothing optional area, on the rock ledges by the lake. (The lower parking lot will take you to the public non-nude beach). There is a restroom facility provided at the lower public parking lot (nudity is not allowed in this area).
BethelThis is a secluded spot with a couple swimming holes, a waterfall, and very clear water. The upper swimming hole is for those who usually wear bathing suits, so climb down the ledge to get to the lower holes where the skinny dipping takes place.
The ledges can be slippery, so if it's wet, walk along the road back towards the two bridges about a 10th of a mile, and then climb down the banking to the water. The upper swimming hole has a natural water slide, so bring a bathing suit if you want to do that. It's right in the forest, so don't set any fires.