and Switzerland. The exception is the old city center of Constance, on the Swiss side of the river. The Seerhein emerged in the last thousands of years, when erosion caused the lake level to be lowered by about 10 meters. Previously, the two lakes formed a single lake, as the name still suggests. Untersee Like in the Obersee, the flow the Rhine can be traced in the Untersee. Here, too, the river water is hardly mixed with the lake water. The northern parts of the Untersee (Lake Zell and Gnadensee) remain virtually unaffected by the flow. The river traverses the southern, which, in isolation, is sometimes called Rhinesee ("Lake Rhine"). The Radolfzeller Aach adds large amounts of water from the Danube system to the Untersee. Reichenau Island was formed at the same time as the Seerhein, when the water level fell to its current level. Lake Untersee is part of the border between Switzerland and Germany, with Germany on the north bank and Switzerland on the south, except both sides are Swiss in Stein am Rhein, where the High Rhine flows out of the lake. High Rhine The Rhine emerges from Lake Constance, flows generally westward, as the Hochrhein, passes the Rhine Falls, and is joined by its major tributary, the Aare. The Aare more than doubles the Rhine's water discharge, to an average of nearly , and provides more than a fifth of the discharge at the Dutch border. The Aare also contains the waters from the summit of Finsteraarhorn, the highest point of the Rhine basin. The Rhine roughly forms the German-Swiss border from Lake Constance with the exceptions of the canton of Schaffhausen and parts of the cantons of Zürich and Basel-Stadt, until it turns north at the so-called Rhine knee at Basel, leaving Switzerland. The High Rhine begins in Stein am Rhein at the western end of the Untersee. Unlike the Alpine Rhine and Upper Rhine, it flows to the west. It descends from 395 m to 252 m. Some stretches of the High Rhine between Stein am Rhein and Eglisau form the border between Switzerland on the south bank and Germany in the north. On other stretches, both sides are Swiss; in fact most of the canton of Schaffhausen is on the north bank. Between Eglisau and Basel, the High Rhine consistently forms the border. The Rhine Falls are situated below Schaffhausen. With an average