Source of the Danube
As early as 1847 the following definition can already be found in the "Universallexikon des Großherzogtums Baden" (Universal Lexicon of the Grand Duchy of Baden): “Danube, the biggest river of Germany, rises at the Martinskapelle in a wild and lonely area of the Black Forest, is called Brege at its origin and forms the river Danube in Donaueschingen where it is unified with the Brigach." (German original: „Donau, der größte Fluß Deutschlands, entspringt bei der Martinskapelle in einer wilden und einsamen Gegend des Schwarzwaldes, heißt am Anfang Brege… und bildet erst in Donaueschingen, wo sie sich mit der Brigach vereinigt, die Donau.“)
Danube Sinkhole
The sinking Danube water disappears into a karst water system of the "well-stratified limestone formation" (the "ox2" layer) of the White Jura and appears again in a horizontal limestone layer (the "ki4" layer), approximately twelve kilometers away at Aachtopf. It then flows as Radolfzeller Aach into Lake Constance at Radolfzell. Thus, a part of the Danube water also flows into the Rhine. This geographical situation is a striking feature of the large European Watershed, which separates the catchment areas of the North Sea and the Black Sea.