Is there a better time to swim than at night when no one else is around? The nice relaxing water, the soft echoes of every movement you make, and the unnerving realization that an unholy creature has just joined you.

Personally, the most terrifying thing is underwater stuff. In a pool it's usually fine as you can see quite clearly. In the open water? Different story. Heck, even video game levels going all the way back to the original Super Mario Bros have always set me on edge. I think it's the restricted movement and the idea that a water creature is literally designed to move well in that environment. What chance do I have?