The Park is located in the drainage basin of the Brda River. One of the main reasons for creating a National Park here was to protect water reservoirs: the Park's territory encompasses 21 lakes (18 of which are larger than 1 ha) whose water is exceptionally clean, since there are neither industries nor farms in the neighborhood. The cleanness of the water is proven by the presence of lobelia (Lobelia Dortmanna, called "stroiczka wodna" in Polish), which is extremely sensitive to pollution and only grows in very clean water.
The Pomeranian Primeval Forest, located in the communities of Chojnice, Koscierzyna, Tuchola and Starogard, constitutes one of the largest forest systems in Poland, covering an area of over 120,000 ha (1.5 per cent of the national territory). The Tucholskie Forests, which belong to this system, are 12.5 thousand years old and are still in a relatively unspoiled shape, although a part of them has been granted the National Park status only recently.
