Lake Constance, a freshwater zungenbecken (or tongue-basin) lake, was formed by the Rhine Glacier during the last Ice Age. The lake is located at the northern foot of the Alps and is found at 395 meters (1,296 feet) above sea level. The third largest lake in Central Europe (after Lake Balaton and Lake Geneva), it serves as a major source of drinking water for southwestern Germany and covers and area of about area of about 540 square kilometers.
Lake Constance is actually made up of three bodies of water: the Obersee (“upper lake”), the Untersee (“lower lake”), and a connecting stretch of the Rhine, called the Seerhein. The Rhine river flows into the lake from the south, which then flows out of the lake to the west
Countries Surrounding Lake Constance
Lake Constance’s shoreline touches three different countries: Germany to the north, Switzerland to the south and Austria at its eastern end. The water body itself contains no borders since there is no legally binding agreement between the three countries. The lake outside the 25-meter isobath is not considered a common area but an area that doesn’t belong to any country. This makes it the only area in Europe that doesn’t have borders.
Daniel-Erasmus Kahn (2004). Die deutschen Staatsgrenzen: rechtshistorische Grundlagen und offene Rechtsfragen (“The German national borders: legal-historical foundations and open legal questions”). Oxford University Press. ISBN 9783161484032.