Or maybe just Walk Underwater. A character is too dense to have any buoyancy, so they deal with bodies of water by walking across the bottom rather than swimming. Actually being able to breathe underwater is optional. Often happens in videogames, where this saves the programmers from having to code for swimming behavior, while averting Super Drowning Skills. Just make the character move slower and jump higher and voila! underwater physics. Compare with Water Is Air.
Hello, Unknown Troper. You'll need to get known to lend a hand here.