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
The Donaubach rises on the castle grounds near the left corner of the front face of the castle Donaueschingen in a karst spring. This karst spring has an embankment of 15 to 70 l/s and enters into the Brigach after flowing 90 meters belowground. The Brigach and the Breg become the Danube after 1.5 km. The source is one of 22 sources in the area of the junction of Brigach and Berg. All of these sources are fed by both water which trickles away above them and rainfall which trickles away on the karstified downs of a landscape called Baar. Together, the Brigach and the Breg empty out between 400 and 1000 l/s.