Eddie, my pond is in Lumberton (TX) and Gypsum worked very well for me. It looked very "lagoonish." That being said, because I still need more grass and vegetation, my pond is muddy again after a good rain. I reapply occasionally.

Which leads me to a question for Bob: Is sheetrock safe to put in a pond? I'm building a house and I have a mountain of sheetrock scraps that I would love to dump in my pond.