The Obersee (English: Upper Lake), also known as Upper Lake Constance, is the much larger of the two parts of Lake Constance, the other part being the Untersee (English: Lower Lake). The two parts are separated by the Bodanrück peninsula. The narrow, northwestern branch of Obersee is also called Überlinger See (English: Lake Überlingen).

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Obersee
View over Lake Constance's Obersee from Winterstaude at dusk
Obersee Show map of Canton of St. Gallen Obersee Show map of Switzerland Obersee Show map of Baden-Württemberg Obersee Show map of Germany Obersee Show map of Austria Obersee Show map of Alps
Location	Tripoint of Germany, Austria and Switzerland
Coordinates	47°37′N 9°26′E
Primary inflows	Alpine Rhine, Bregenzer Ach, Argen, Alter Rhein (Fußacher Durchstich), Schussen, Dornbirner Ach, Seefelder Aach, Rotach, Stockacher Aach and smaller streams
Primary outflows	Seerhein
Max. length	63 kilometres (39 mi)[1]
Max. width	14 kilometres (8.7 mi)[1]
Surface area	472 square kilometres (182 sq mi)[2]
Average depth	101 metres (331 ft)[2]
Max. depth	251 metres (823 ft)[2]
Water volume	47.6 cubic kilometres (11.4 cu mi)[2]
Shore length1	186 kilometres (116 mi)[2]
Surface elevation	395.33 metres (1,297.0 ft)
Islands	Lindau, Mainau
Settlements	Überlingen, Meersburg, Friedrichshafen, Lindau, Bregenz, Rorschach, Konstanz
1 Shore length is not a well-defined measure.

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The Obersee has an area of 473 km² (183 sq mi) in size and extends for 63 km (39 mi) between Bregenz in the Southeast and Bodman-Ludwigshafen in the Northwest. Its maximum width is 14 km (8.7 mi). Its main inflow is the Alpine Rhine, with other tributaries being the Dornbirner Ach, Bregenzer Ach, Leiblach, Argen, Schussen, Rotach, Seefelder Aach, Stockacher Aach and Aach. At Konstanz (Constance), it drains through the Seerhein into the Untersee.

The distinctive, northwestern arm and 21 square kilometres (8.1 sq mi)-large Lake Überlingen (Standard German of Germany: Überlinger See), named after Überlingen, is part of the Upper Lake Constance, as well as the Bay of Bregenz, and the Constance Hopper.

The countries that border the lake are Switzerland, with its cantons of Thurgau and St. Gallen, Austria, with its federal state of Vorarlberg, and Germany, with its federal states of Baden-Württemberg and Bavaria. The exact location of the border between the riparian states within the south-eastern part of Obersee have never been jointly agreed upon (see Lake Constance); only the smaller northwestern water of Lake Überlingen is completely within German territory.

The southeastern end of the lake borders the Alps, the Appenzell Alps of Switzerland and the Allgäu Alps of Austria and Germany. A notable mountain with outlook is the Pfänder above Bregenz.

The Romans called it Lacus Venetus, Lacus Brigantinus and Lacus Constantinus. In the Middle Ages the dominant term was Lacus Bodamicus, or in German Bodensee.^{[citation needed]} Gradually, this name began to include the Lower Lake (Lacus Acronius), so the term "Upper Lake" was introduced for the larger lake.^{[dubious – discuss]}

• Untersee (Lake Constance)
• Seerhein
• Bodanrück