Very well done. The music really helps build the tension. Sound effects and voice over are really nice. I also like the logo/splash screen a lot (though it did stretch weirdly and looked very pixelated on my screen).
From a UX point of view I think it would've been nice if looking around was controlled using the mouse (or it could be a configurable option in a more polished version).
Maybe another thing to add for increased difficulty/chaos would be fish that aren't as deterministic as the ones in this version. Although I must admit the current behavior really drives home that feeling of inevitability you get from movies like "Jaws".