Flatten blue non-hardening clay or a combination of blue and green clay on the flat surface. Don't worry about trying to make it look smooth. Press down the clay with your thumbs and leave small divots in the clay, which will create an illusion of waves. Completely cover the surface of your plane with the clay.
Apply paint to the clay once it has dried. Add different hues to the surface. For instance, rather than it being one solid color block, use a diluted navy blue paint. Start spreading and covering your surface with navy blue paint using a spackling knife.
Load some of your paint from your palette onto your spackling knife and swipe over an area of your plane like you would when applying blotches of paint. Reswipe the same area but with your blade more vertically angled to your plane. These movements create a thick texture and add dimension to your plane.
Layer the colors for added effect. Don't mix the paint because you want to apply it in layers so both colors come through. Instead, apply one color, let it dry, and go over it with the other color.
Create the effect of light reflection by adding a small sprinkling of glitter to your ocean floor. Once the paint has dried and settled, apply a thin layer of liquid glue to the surface using a paint brush. Sprinkle silver glitter on the surface. Avoid letting the glitter clump by brushing it with a soft paint brush. You are aiming for a shimmering effect and not a noticeable glob of colored glitter.