Wielkopolska belongs to the regions with the poorest water resources both on Polish and European scales. This region features the lowest precipitation in Poland. Water resources in rivers running across Wielkopolska are also small. A considerable fraction of water resources is in lakes, but they are distributed unevenly, with the prevailing fraction in the northern, part of the region. Generally, more than 70% of river length are outside any water purity classification. Water contamination in lakes, especially larger ones, is not good, either. Small lakes siuated in forests, which are not used for recreation, have the purest water. Safe swimming is possible only in every fifth lake of Wielkopolska.