Danube
The Danube was once a long-standing frontier of the Roman Empire, and today flows through 10 countries, more than any other river in the world. Originating in Germany, the Danube flows southeast for , passing through or bordering Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine before draining into the Black Sea. Its drainage basin extends into nine more countries. The Danube river basin is home to fish species such as pike, zander, huchen, Wels catfish, burbot and tench. It is also home to a large diversity of carp and sturgeon, as well as salmon and trout. A few species of euryhaline fish, such as European seabass, mullet, and eel, inhabit the Danube delta and the lower portion of the river.
Source of the Danube
There was an active rivalry between the municipalities of Furtwangen and Donaueschingen for the claim of being home to the "official" source of the Danube since the 1950s, sometimes with the involvement of the government of the state of Baden-Württemberg. 
Thus, in 1981 the state government granted Donaueschingen the request that the source in Furtwangen should no longer be labelled "Donauquelle" in official maps.