The third construction is a little sledge. Two runners and a place to sit. Since the series of Lego Classic had no snow, attempting to swim on those sledge seems to be the best solution.
It floats on the water. Well, but the drive is not there, so it will be hard to swim. In addition to the sledge you can do an additional small hovercraft visible in the background from remaining bricks! Has been added as a separate alternative.