I'd animate a texture map. Shoe String Graphics (http://www.des-web.net/html/shoestring_shaders.html) has a shader called Proximity which would make this much easier. They haven't released an update for C6 yet however. If you're still using C5, then it won't be an isue though. Another option is to create a movie effect with any of the vide special effects softtwares out there and import as a texture onto a vertex object that is just slightly above the other water in your scene.