Yeah, I get what you're trying to do with the shadows, but it really wouldn't make sense unless you can see details of the bottom(sand, coral, fish, crabs, rocks, whatever…). With the kind of symbolic blue it's just confusing. Even with more realistically depicted water the deeper the water, the more caustics would obliterate the shadows. Rather than depending on shadows, maybe reflections on the water surface? Definitely the reflections or major shadows should be on the surface.