The Blue Lagoon received its name from the movie of the same name, and it sounds better than "Blue Accidental Lake", which doesn't roll off the tongue in quite the same way. Indeed, the lake is an accident - when the hydro-electic plant was built, the outgoing water was expected to flow down the stream, but sediment settled at the stream mouth, slowing greatly the current, and a lake formed. The water is bright blue, owing to something in the rock, and is apparently very good for people, and because it is outgoing water from the hydro-electric plant, it is also mostly very warm. We went for what was intended to be a brief swim, but the water was so pleasantly warm, that we stayed until long after we became wrinkly. And it hailed.