Not to nitpick or anything, but I actually submitted mine first, so that one is a duplicate.

EDIT: After loading the campaign again, the bug is slightly different. It seems that using turbo while at the surface of the water should automatically submerge you. I'll test more for how I was able to stay at the surface.

At the time when I reported it, there were a lot of other bugs that actually interfered with playing the game. If most of the issues now are just cosmetic, I'll bump up the severity.
EDIT: I guess I can't adjust the severity. In any case, it's already been reviewed, so the severity at this point doesn't matter that much.

Updated. This bug makes me feel so popular.

Txontirea fixed it for me. I had assumed all of my shots were missing, even at close range, but changing ammo types fixed the issue.