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.
Baar (region)
The Baar contains the source of the Neckar (a bog in Villingen-Schwenningen) and the Danube. The sources of the Danube, the Brigach and Breg, originate in Furtwangen im Schwarzwald and Sankt Georgen im Schwarzwald and join the smaller Donaubach in Donaueschingen.