I was playing my survival world when I stumble across a small pot of water in a cave, so I dived into It and couldn't see anything (the screen was all blue!) at all, plus there was a awkward gray square in the cursor when underwater!
This really affects underwater gamplay a lot, I can't even mine in aquifers!

Steps to reproduce:
1. Go to Y level 52 or less (I'm not too sure if It affects more positive Y levels)
2. Get inside some water in the level