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.“)
The Ister (film)
Eventually the film arrives at Donaueschingen, and at the Breg and the Brigach, the two tributaries whose confluence marks the point at which the river becomes known as the Danube. The film then travels upstream along the Breg, past Vöhrenbach and Furtwangen, in search of the "true" mountain source of the Danube.