Natural Swimming Pools.

Steven Kurutz of the New York Times writes:

Natural swimming pools (or swimming ponds, as they are called in
Europe, where the concept originated 20 years ago) are self-cleaning
pools that combine swimming areas and water gardens. Materials and
designs vary — the pools can be lined with rubber or reinforced
polyethylene, as in the case of Total Habitat’s, and may look rustic or
modern — but all natural pools rely on “regeneration” zones, areas
given over to aquatic plants that act as organic cleansers.

The pools have skimmers and pumps that circulate the water through the regeneration zone and draw it across a wall of rocks, loose gravel or tiles, to which friendly bacteria attach, serving as an additional biological filter. Unlike artificial ponds, which tend to be as murky with groundwater runoff and sediment from soil erosion as the natural ponds they’re modeled on, in a natural pool the water is clear enough to see through to the bottom.

The pools, which cost about the same as or slightly more than conventional ones, depending on landscaping, appeal to gardeners because of the great variety of plant life that can be grown in them, as well as to green advocates and others who don’t want to swim in chlorinated water.

Photo credit: Sandy Huffraker for The New York Times