What we need in Bryce 5 or whatever for underwater scsnes is a type of water surface tyat behaves like the real thing :: it has a refractive index (default = that of water); it can be in waves read from a map or created by any suityable type of noise; it reflects / diffuses / transmits / refracts light like the real thing. Then "caustics" etc will take care of themselves. - When scuba diving in the Red Sea in Aug 1999, I did not see refraction caustics except in very shallow water. But we sure need a proper way to make a wavy sea surface as seen from underneath.

And find how much it would affect realism if we allow each ray of light to me affected once only by it, to save on render time.