Hello, I think one thing that makes underwater scenes look beliveable is the way light is defracted because of the movement of the water.

Susie, can I ask how deep is the water? Can the surface be seen? Is it shallow enough to have the light of the sun shown off of the bottom sand?

Maybe you can review some of the images done in Bryce or Vue in their galleries and see if there are some good examples.

I'm sure it can be done in Photoshop but I think you would appreciate the effects done with these 3D programs.

yo