[Soukup]

use volumetrix lighting.

basically you can just add a fog effect to the whole image. And set the density to a very low number. Then use a couple spotlights and point them at the ground and add some volumetric lighting to them. If you have the lights low enough and the fog high enough, if should work out great. Also u can add a couple bubbles by adding a particle array, and then selecting the bubble preset. You can then add a pre-existing raytrace bubble material from the material library and *BAM* a frigging realistic rendering!