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.
https://en.wikipedia.org/wiki/Lake_Constance