Natural Swimming Pool/Ponds (NSP's) are a chemical-free, low-maintenance alternative to traditional chlorine pools. The water is clean, crystal-clear, and filtered naturally using a built-in biological filter. by kathrine
DIY natural swimming pool - the video provided in the link is pretty cool. I've had dreams of these things, and now that I've seen an actual video I'm a bit kreeped out because I don't like swimming in dark water, but the pool itself is pretty awesome
Here's a great example of a conventional pool turned into a natural swimming pond. They offer a much lower maintenance alternative to conventional pools and allow you to swim in clean, chemical free water.