Natural swimming pools (NSPs) are a way to blend the sustainability & natural beauty of a pond with the functionality of a swimming pool. NSPs use biological filtration in lieu of the more common chemical or chlorine water cleaning systems used in most artificial swimming pools. The pools generally consist of a swimming area & a filtration area which can interact & be visible as much or as little as the designer wishes. The pools have a tendency to look more natural than completely artificial pools but can be made to look extremely contemporary as is evidenced in the images below. To date there are over 20,000 NSPs in Europe although there are none to date in the US.