How to build a natural swimming pool:
in recent years, a few builders and a growing number of homeowners have learned how to build pools without relying on a mass of manufactured materials and chemical additives. They’ve found it’s possible to construct pools that are more about building with nature and blending into the natural landscape. Natural swimming pools use gravel stone and clay in place of concrete or fiberglass, and aquatic plants instead of harmful chemicals and complicated mechanical filtering systems. The plants enrich the pool with oxygen, support beneficial bacteria that consume debris and potentially harmful organisms, and give habitat to frogs, dragonflies and other water life. The result is a beautiful, ecologically diverse system that is relatively inexpensive to construct. (A natural pool can he constructed for as little as $2,000 if you do it yourself, while conventional pools can cost tens of thousands of dollars.) Natural swimming pools require no harmful chemIcals, are fairly low-tech, and once established call for only a modicum of management. You won’t have to drain the pool each autumn. Except for topping it off now and then, you’ll fill the pool only once. Read more: http://www.motherearthnews.com/Do-It-Yourself/2002-08-01/Natural-Swimming-Pool.aspx#ixzz1SAGT8KYX
Here’s a cool slide show of these sort of pools.
A couple more pics: