This is one of the best pieces I've seen so far, great detail, a nice calm setting and interesting perspective.
The design is pretty strong and doesn't fall prey to the whole 'copy/paste' style of design I see a lot of people doing, I love the realistic approach you've gone for.
A couple of crits though:
The light shining through the water would refract and play over the creature (google underwater light refraction if you are unsure of what I mean). If you are able to add these then it would bring more life and realism to this already great piece.
The underside of the creature should be getting softer and as it is being obscured by the water, take on a subtle blue tint along the lighter part of it's neck. I see you started doing that really lightly where the neck meets the body but it should start at the jaw and get stronger from there.
Hope that made sense and helped you a bit haha.
Great piece and good luck :)