It's a great game game, but it could do with some improvements!
1. The Upward force, buoyancy is too strong. The only way to go down is to cling to walls.
2. You could add some other types of platforms, such as ones that trap you, ones that attract you, ones that bounce you etc.
3. You can also add oceanic Currents, that push the player (and other things, hint hint!) into a certain direction
Otherwise, It's a great game!