I swam competitively for.... 7 or 8 years, so I'm a very strong swimmer.
However, I am still utterly terrified of exceptionally deep water, or water where you can't see the bottom. (Lakes, Oceans once you're away from shore, Rivers)
Going down this pipe to the boss fight, I damn near had an anxiety attack, because this is EXACTLY the kind of thing that terrifies me. Like, if you were to make an underwater version of Amnesia and told me you'd pay me a million bucks to complete it, I don't know if I'd mentally be able to handle it. Freaking 'Amnesia: Marianas Trench' would be one game I could never finish.