What basin does the lake that the Argen river flows into belong to?
Argen: The Argen is a river in Baden-Württemberg, Germany. Argen:  It flows into Lake Constance between Kressbronn am Bodensee and Langenargen as the third largest tributary to the lake. Lake Constance: 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". Lake Constance:  These waterbodies lie within the Lake Constance Basin ("Bodenseebecken"), which is part of the Alpine Foreland and through which the Rhine flows.
Lake Constance Basin