Lake Constance (German: Bodensee) is a lake on the Rhine at the northern foot of the Alps, and consists of three bodies of water: the Obersee or Upper Lake Constance, the Untersee or Lower Lake Constance, and a connecting stretch of the Rhine, called the Seerhein. These waterbodies lie within the Lake Constance Basin (Bodenseebecken), which is part of the Alpine Foreland and through which the Rhine flows.
The lake is situated in Germany, Switzerland, and Austria. Its shorelines lie in the German states of Bavaria and Baden-Württemberg, the Austrian state of Vorarlberg, and the Swiss cantons of Thurgau, St. Gallen, and Schaffhausen. The Rhine flows into the lake from the south, with its original course forming the Austro-Swiss border, and has its outflow on the “Lower Lake” where — except for Schaffhausen — it forms the German-Swiss border until the city of Basel.