This was a cool short entry, the themes were implemented very well, and I think you you did well making the looting feel pressured but not insanely stressful.
I do agree with other comments mentioning it would be nice if the air meter could refill if you reach a non-filled level though. Further forcing the player to decide between sticking down and searching for loot or going back up for air.
I though the turning speed could be bumped up a little bit, but overall movement felt good.
Also is the chicken idol randomly placed? I swear the first 3 times I played through I scoured the map and couldn't find it at all.
The audio and visual effects for the rising water were good, though personally I think a few more splashing/water rushing sounds would be nice. I thought the flashlight following cursor was an interesting idea too, I think it worked well. I especially liked the Quake-like sin wave effect for being underwater.
I thought the little alien creature in the main menu running across the screenw as funny too.
Overall I liked the core loop, and I liked the atmosphere and visuals.
Good job!