In an ecological swimming pool, 'eco pool' or 'bio pool', we do not use chemicals to keep the water clean but water plants and cane. Much better for the environment and more enjoyable to swim (no chlorine).
Want to kno more about eco pools? Here is a BBC report about
natural swimming pools:
If you are interested in the technology
geïnteresseerd there is a lot of information on internet,
amongst others this
article in Mother Earth News