It seems like I've completed every room in this area, but I still can't manage to grab the water element from beneath the crab like creature. How do I get it? Bonus points for giving a hint and putting the full answer in spoiler text, I really like to figure things out myself!
The hint is: There is something underwater you must attach to your sub.
In the upper left corner of the underwater area, there is a creature with a tentacle-esque appendage that can be attached to your submarine. Once the tentacle is attached, float down to the crab, remove the tentacle and attach it to said crab. Voila. The element is yours.