There's something about water that I never want to traverse through it. In a nonflying zone I sometimes even go the long way around a lake rather than swim through. It's always been like this, even in 2D platformers of early 90's. The flora isn't to my liking either, same with the fauna, they just don't appeal to me. I love air, the freedom and lack of restriction of it, so perhaps that's why I don't like underwater.
I do like surface water themes, though. Islands, seafaring, ships, porttowns, pirates etc. those I love.