When properly designed, the garden lake has a self-cleaning function.
In the shoals, which should account at least for 1/3 of the water level, the plants are set in order to clean the water by absorbing nutriments from it. These plants are also used in root based water treatment facilities.
The usual size of a garden lake is 70 m2 or more, the depth of the swimming zone is at least 2m. The lake then does not get overheated and functions as a biotope.
The water does not go off, and neither algae nor cyanobacteria vegatete in it. If you want to have the lake transparent for swimming, it is good to use a mechanical filtration on a sieve basis, so that the mechanical contaminants such as fallen leaves get filtered out. The pure water then flows back to the lake.
On small grounds with no space for a large water area, it is possible to design also a smaller lake, e.g. from 40m2. In such case, efficient mechanical filtration must be used.
It is recommended to use app. twice a year a water vacuum cleaner to clean the sides and the bottom of the lake, in order attain absolute clearliness of the water.
The water shall not be drained from the lake for winter. It is enough to lower the level of water a little bit.