I understand what the OP means about water being clearer. However, one thing that annoyed me (in all Bethesda games) is how you can see to the bottom of any body of water. I want it to be too dark to do this. Also there should be apparatuses to take us deep in water. Submarine-like machines that move very slowly that only see a few feet in front of them. That or magic to help us breath under water. Swimming in water should be slowed tremendously.

I just want there to be more going on under water in general, give us a reason to use that water breathing spell. Morrowind had plenty of shipwrecks and submerged ruins, in Oblivion there was, um, a few chests and the entrance to what's-his-face's tower, with a couple short expanses of other dungeons under water.

Boats that go boating, giant ice bergs that have cave systems in them. far off islands you can't see unless you go sailing. And large sea creatures! http://www.youtube.com/watch?v=Ua8kj-JdakE

scale of some of our earlier earth monsters> http://img42.imageshack.us/img42/9964/seacreatures.jpg