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.
Upper Danube Nature Park
The Upper Danube Nature Park (German: "Naturpark Obere Donau"), founded in 1980, is located in the south of Baden-Württemberg in Germany and encloses primarily the districts of Tuttlingen and Sigmaringen. It encompassed initially 860 km that were increased by about 500 km in 2005. The headquarters of the nature reserve association is at Beuron. The highest proportion of the nature park is taken up by the Heuberg, the south-western plateau of the Swabian Alb, and is punctuated by the Danube.