Great start. Overall you might try enhancing the atmospherics/distance effects. The current effects has little depth because the mountain top and the fish share the same level of lights and darks. In a related comment, the green on the trees is a little hot/bright. Toning that down will prevent it from becoming the focus of the image like it is now because of it's intensity. For the water, maybe making the water less transparent. Then add several spot lights with water caustic gels punching up the dark and light areas under the water surface. Also, you might try using the particle generator to create some underwater floating "stuff". You can create an irregular alpha mask for the particles so they don't look geometric. The water is fairly turbulent. A large boulder or two might provide a "visual excuse" for the turbulence. Just the mad ravings of a lunatic illustrator.... ;-)