Natural Swimming Pool

A natural swimming pool is a pond built for swimming, kept clean by plants rather than chemicals. Beside the open swim zone lies a shallower basin thick with water plants, the regeneration zone, and water moves between the two. That planting takes up the nitrogen and phosphorus that would otherwise feed algae, so the water clears without chlorine or any other disinfectant.

Nutrient poverty is therefore the governing requirement, the opposite of how every other pond is managed, and traces matter: total phosphorus above 0.025 mg per litre is read as pollution. The ground around the pool counts as much as the pool. It cannot sit downhill of a septic field, a barnyard or fertilised ground, and keeping runoff out belongs to the build: a permanent strip of vegetation around the water, with ditches and grading to send dirty flow elsewhere. The regeneration zone is sized against the swim zone and cleans that water only. Excavation, liner and planted filter together are beyond hand tools though short of a licensed trade.

What goes wrong is rarely visible. Warm, calm, sunlit water carrying spare nutrients is the recipe for a bloom of cyanobacteria, some of which make toxins causing skin rashes, stomach upsets and breathing trouble, and they can outlast the scum that announced them; the rule is to stay out whenever a bloom is suspected rather than wait for proof. Waterfowl on a small pond, or one storm washing runoff in, can carry bacteria past the swimming limit of 126 E. coli colonies per 100 mL within a day without changing how the water looks. Swimmer's itch, from a parasite that burrows into the skin, is a lesser nuisance held down by controlling the snails it needs. Upkeep is testing rather than cleaning: a certified laboratory sample before each swimming season, frequent bacterial tests through it, and the water closed whenever it turns cloudy, foul-smelling or green.