Thanks for the ideas. I tried doing multiple planes for the water to get a good fit around the edge of Crater Lake, and then grouped all the planes. Applied the water texture to the grouped planes and it looked fine, just like a single continuous surface. Seems to be a quick way to do it. It's fine for simple surface views of a lake. Not sure I understand how to do the method quoted by Jaywat. If I had two DEM's of the same dimensions and resolution, then the idea of Bop would work fine too. It's all experimentation and eventually solutions come up! It would be simpler if there was an option to do a polygon shape for the plane! If there are other ideas on this matter I'd be interested to hear of them. Lester