Natural swimming pools take a bit of forethoughtbut can be well worth it in the end. Gravel, stone and clay are used in place of concrete or fiberglass, and aquatic plants and a simple aeration system is all that’s needed to keep the water clean. This cross-section shows the plant zone and swimming area of a natural pond. After compacting a thin layer of soil, a liner and gravel are applied to the pond’s bottom. A floating dock equipped with a ladder provides easy access to the pool.