The relief of the site has been finally shaped during the Baltic glacial period which left deep gullies and ice melting holes between moraines, later filled in by lakes. Local differences in elevations reach up to 50 m. Many of the smaller lakes have been transformed into peatbogs (raised mires) with peat layers of various depths and diverse vegetation cover. Thickness of glacial formations – clay, sand and gravel locally exceeds 150 m. The Lake Wigry of 2.163 ha surface and maximal depth of 73 m remains in close hydrological contact with most of the smaller lakes. Pierty is the second larger lake of a surface of 228 ha and 38 m deep. The lakes display a variety of features of trophic status of water. Separate group constitute mid-forest dystrophic lakes whose dark water is highly saturated with organic substances. The dystrophic lakes have been developed in the process of lake overgrowing.