Danube
"Danube" is an Old European river name derived from a Proto-Indo-European "*dānu". Other river names from the same root include the Dunaj, Dzvina/Daugava, Don, Donets, Dnieper, Dniestr, Dysna, Tana and Tuoni. In Rigvedic Sanskrit, "dānu" means "fluid, drop", in Avestan, the same word means "river". In the Rigveda, "Dānu" once appears as the mother of Vrtra, "a dragon blocking the course of the rivers." The Finnish word for Danube is Tonava, which is most likely derived from the word for the river in Swedish and German, "Donau". Its Sámi name "Deatnu" means "Great River". It is possible that "dānu" in Scythian as in Avestan was a generic word for "river": "Dnieper" and "Dniestr", from "Danapris" and "Danastius", are presumed to continue Scythian "*dānu apara" "far river" and "*dānu nazdya-" "near river", respectively.
Wutach (river)
The lower Wutach flows along the line of the valley once occupied by the much more powerful upper Ancient Danube ("Urdonau"), but in the opposite direction. At the turn of the Miocene/Pliocene epochs, at a time when the Black Forest was already being uplifted but the Rhine Graben was not as low as it is today, the Danube had its source in the area of what is today the upper Rhone. This river system fragmented and most of it gradually became a network of tributaries of the Rhine river system (For more information, see Wutach Gorge). Latterly, the upper and middle reaches of today's Wutach formed the Feldberg Danube, the upper course of the Danube. But after the watershed between the aggraded Feldberg Danube and the downward-cutting Ancient Wutach, which existed until the last ice age, had been severely eroded, the Feldberg Danube broke out to the south-west into the Rhine valley some 20,000 to 70,000 years ago, forming the striking "Wutachknie" at Blumberg. Because of the relatively steep gradient in its new direction of flow towards the Rhine, the river carved out the deep, roughly 30-kilometre-long, Wutach Gorge into the plateau, a process that continues today. It has excavated about two cubic kilometres of rock. The valley slopes tend to slip; this makes the Wutach Gorge even more of a transportation obstacle than its, in places, steep relief would suggest and makes the maintenance of roads and tracks, and even of hiking trails, expensive.