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.