PabloS - there are two different foam effects here. One is from the ray bias - this is making the foam at the water's edge where it touches the sand. I think it only happens when the underlying surface is at a very small angle to the water. The other foam is from the fBm node. In post 23, I turned that off, so you can see only raybias foam in that render. You don't have to use the fBm node. You could actually draw the foam and use an image mask instead. Hmmm, give me a minute and I'll demo that.

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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)