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 ("upper lake"), the Untersee ("lower lake"), and a connecting stretch of the Rhine, called the Seerhein.
The lake is situated in Germany, Switzerland and Austria near the Alps. Specifically, its shorelines lie in the German federal states of Bavaria and Baden-Württemberg, the Austrian federal state of Vorarlberg, and the Swiss cantons of Thurgau, St. Gallen and Schaffhausen. The Rhine flows into it from the south, with its original course forming the Austro-Swiss frontier.
Freshwater Lake Constance is Central Europe's third largest, after Lake Balaton and Lake Geneva. It is 63 km (39 mi) long, and at its widest point, nearly 14 km (8.7 mi). It covers approximately 571 km2 (220 sq mi), and is 395 m (1,296 ft) above sea level. The greatest depth is 252 metres (827 ft) in the middle of the eastern part (Obersee). Its volume is approximately 10×109 m3 (13×109 cu yd). The lake has four parts: the main section, called Obersee, 476 km2 (184 sq mi); the north section, Überlinger See, 61 km2 (24 sq mi); the west section, Untersee, 63 km2 (24 sq mi); and the northwest section, the Zeller See and Gnadensee. The regulated Rhine flows into the lake in the southeast, through the Obersee, the city of Konstanz and the Untersee, and flows out near Stein am Rhein. Lake Constance provides fresh water to many cities in south Germany. The culminating point of the lake's drainage basin is the Tödi at 3,614 metres above sea level.
The lake itself is an important drinking water source for southwestern Germany, called Bodensee-Wasserversorgung ("Lake Constance Water Supply"). Car ferries link Romanshorn to Friedrichshafen, and Konstanz to Meersburg.Source: Wikipedia