Seerhein in the context of Obersee (Lake Constance)

Lake Constance (German: Bodensee, pronounced [ˈboːdn̩zeː] ) refers to three bodies of water on the Rhine at the northern foot of the Alps: Upper Lake Constance (Obersee), Lower Lake Constance (Untersee), and a connecting stretch of the Rhine, called the Seerhein (lit. 'Rhine of the lake(s)'). These waterbodies lie within the Lake Constance Basin (Bodenseebecken) in the Alpine Foreland through which the Rhine flows. The nearby Mindelsee is not considered part of Lake Constance.The lake is situated where Germany, Switzerland, and Austria meet. Its shorelines lie in the German states of Baden-Württemberg and Bavaria; the Swiss cantons of St. Gallen, Thurgau, and Schaffhausen; and the Austrian state of Vorarlberg. The actual locations of the country borders within the lake are disputed, with Austria, Germany and Switzerland all holding different opinions on the matter.

The Alpine Rhine forms, in its original course (Alter Rhein), the Austro-Swiss border and flows into the lake from the south. The High Rhine flows westbound out of the lake and forms (with the exception of the Canton of Schaffhausen, Rafzerfeld and Basel-Stadt) the German-Swiss border as far as to the city of Basel. The Leiblach forms the Austria–Germany border east of the lake.

The border between the modern states of Germany and Switzerland extends to 362 kilometres (225 mi), mostly following Lake Constance and the High Rhine (Hochrhein), with territories to the north mostly belonging to Germany and territories to the south mainly to Switzerland. Exceptions are the Swiss canton of Schaffhausen, the Rafzerfeld and hamlet of Nohl of the canton of Zürich, Bettingen and Riehen municipalities and part of the city of Basel in the canton of Basel-City (these regions of Switzerland all lie north of the High Rhine) and the old town of the German city of Konstanz, which is located south of the Seerhein. The canton of Schaffhausen is located almost entirely on the northern side of the High Rhine, with the exception of the southern part of the municipality of Stein am Rhein. The German municipality of Büsingen am Hochrhein is an enclave surrounded by Swiss territory.

Bodanrück (lit. 'Bodan rise') is the 112 km (43 sq mi) wide peninsula that divides Lake Constance (Bodensee) into Überlinger See (part of Obersee) and Gnadensee, which is part of Untersee. At its southern end, it reaches the Seerhein, which links Obersee with Untersee.

It is bordered by the island of Mainau to the east and Triboldingerbohl and Reichenau Islands to the west. The Markelfinger Winkel separates it from the Mettnau peninsula. The nature reserve Wollmatinger Ried lies at the southern shore of Bodanrück. Mindelsee is a small lake located on the peninsula.