Hmm, well, I don't particularly like the water, but it's always something I've been able to get over. I'm not the best swimmer, so I expect that's why I don't like being in the water; lack of control. It freaks me out in video games worse than in reality, until I can be sure I know exactly how many fishy monsters are in the water and where they are, I hate being underwater in video games. I also had a fear of sharks for a while, that probably ties into it.
I guess I might be more afraid of things getting me in the water than anything else. That combined with a lack of control makes me on edge in and under the water. (Which is ironic given I apparently live under the sea. Okay, so it matched a past avatar of mine and I haven't bothered to change it. )
I also started reading Edgar Allen Poe when I was around 12, and since then I've had a fear of being buried alive. Fortunately it's pretty unlikely, but it still creeps me out. Once I'd found out that scratch marks had been found on the inside of coffins before the 20th century I was pretty thankful that they drain your blood before burying you nowadays. (Though there's still the possibility of waking up in the morgue before that, I suppose. Even with all today's medical achievements there's still room for error.)