The Mathisleweiher is a large bog lake, under 2 hectares in area, in the Black Forest in southern Germany. It lies in the High Black Forest between Feldberg in the west and the Titisee in the east on the territory of Hinterzarten at about NN southwest of the village in the Eschengrundmoos Nature Reserve. The pond impounds the Zartenbach which flows through it from west-southwest to east-northeast. The stream rises on the eastern slopes of the Ramselehöhe ( NN) at about NN, picks up the Eschengrundmoosbach from the right from the protected bog and runs for less than a kilometre before entering the lake. A shorter stream runs from the north from the woods of the Stuckwald. It has a catchment of 1.0 km2