In the old days, we used to swim in lakes, or ponds. A European trend of man made swimming holes may to be gaining ground in North America. The New York Times has a feature article on these self-cleaning ponds, which combine swimming areas and water gardens. Water quality is ensured thanks to an engineered system which uses, among other things, plants and algae for natural filtration.
Implications - The benefit of having a man-made, self-cleaning body of water to swim in is that the water quality is of the very highest and, in some ways, mimics a natural body of water. Hopefully these will become increasingly popular.