With a length of 14 kilometers, the Ruppiner See is the longest lake in the state of Brandenburg. It has a maximum width of 800 meters and its deepest point is about 24 meters. In addition to the towns of Neuruppin and Alt Ruppin, the towns of Gildenhall, Gnewikow, Seehof, Karwe, Wustrau and Altfriesack are right on the lake. Neuruppin is the district town of the district of Ostprignitz-Ruppin and the traditional capital of .