I created a tank of glass 10x10x6 filled with water on a creative/superflat world.  No matter how long I stay underwater I can not see all the way across the tank (neither the glass or a sea pickle I place on the opposite side of the tank.  I do not see similar issues in creative on a normal world.  I have also tested with 3 status effects (night vision, water breathing and conduit power) and all 3 have no effect good or bad.