when swimming at sea level you cant see the world sky or above the water view.

so when swimming around in the game. you normaly can see the world when your above you can when your below water you can. but that middle point when you can just swim at the water level you cant unless you are really close. it makes the world around you almost invisible. 

its darkened like your under water but you cant see above well makes swimming hard in this beta due to your sence of destination is gone.