These are the natural pools in Radotín and Lhotka, which function on the principle of organic filtration. How do natural pools differ from artificial pools? A natural pool is an artificial water reservoir with a natural appearance that is biologically purified, without any chemicals, only using plants and ecosystems in regeneration zones – water reservoirs built near the natural pool. Swimming is suitable not only for families with small children, but also for those suffering from allergies who would be bothered by the chlorine in a regular swimming pool. The limitation is the size of the natural pool. They are not suitable for big cities due to the smaller capacity. However, they have slowly started to emerge in the suburbs, and Prague already has two.