The water is just as clear at 100m depth as it is at 10m or 1m. This is a missed opportunity for a great immersion making effect that is sure to spellbind new players. By making the water turn rapidly darker as you descend downwards you can give players a great feeling of diving deeper and make them "experience" the increasing masses of water that is above them. Sitting at 50m underwater and seeing a bright blue water fog is very immersion breaking. At this point the water should be very dark since it is blocking the sun.

Images:
http://i.imgur.com/G135E1fh.png - location
http://i.imgur.com/EFVT5Skh.jpg - ocean floor on that location

There is big depth in the ocean on the location shown on the first image, but there is too much light on the bottom (may be darker with bigger depth?)