To get realism under the water, we have to do much more. We have to simulate the effects of the missing volumetric lighting equations. All I did here was move the camera. It's not going to give the volumetric lighting and floating particle attenuation.

Poser doesn't have any of that. I will show you how to add all of it.

Notice, also, that Poser doesn't know how to do the reflections from under the water surface correctly. This is a sore point with me. But no matter. I will show how to get them.

If you don't want to follow the math, you can skip, as I will be supplying the shaders. But there is a lot of math and knowing it will help you deal with realism in other situations.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)