Bodies only float once they have gassed up which takes awhile. If on Scuba gear, because of lobster, starfish and other marine creatures eating the exposed parts of the body, the body itself, even if not weighted down with gear, may never float up since the skin has already been punctured by the fish and released the gases. In a lake, where there are no scavenger creatures like lobsters and such, the body will usually float eventually. I have had to pull my share of bodies up to the surface when I was a search and recovery diver for the Sheriffs Dept in San Diego.
Steve