I think it's pretty cool that you were able to put in the concept of limited ammo! I was amused to find that shooting a harpoon at a harpoon pickup actually picks up those harpoons, haha. The theme and aesthetics are great. My only complaint is that WASD movement felt a bit frustrating to control.
I think that you have the right idea with how to do the water physics, it's just that the execution of it was severe. A little tweaking would clear it up pretty quickly, I think!