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.
Danube-Auen National Park
Until the 19th century the Danube was an untamed river. In the 19th century, extensive engineering began to alter the natural balance of the river landscape dramatically. Many side-channels were dammed so that they now carry water from the Danube only at flood stages. Ever more intrusive engineering interventions were accompanied by decades of heavy forestry use in many parts of lowland forests. In the 1950s, development began of an nearly unbroken chain of hydroelectric power plants and associated dams on the Austrian section of the Danube River.