Beautifully done underwater world! Music was simple, but added appropriately to the atmosphere. The mechanic was fun too. Only comment I have is the mouse "look" was literal, I think a "lerp" to rotate the camera would chill that out and polish it up.
I did get some sort of collider issue in the wall and got stuck here:
That was simple enough to avoid, so I kept playing and enjoyed it, but for your debugging pleasure :).