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.
Wachau
The Danube valley in Austria between the cities of Melk and Krems in Lower Austria is called the Wachau. This stretch of the valley includes the hills and the adjacent Dunkelsteiner Wald (Dunkelsteiner Forest) and the southern Waldviertel. The Danube river flows north-northeast from Melk to Dürnstein through a meander from which it flows southeast, then east past the city of Krems. In the Wachau, the town of Spitz lies on the Danube's western bank and the city of Melk on its eastern bank. Other important towns in the valley are Dürnstein, Weißenkirchen in der Wachau and Emmersdorf an der Donau, which have a galaxy of old homestead buildings dating from the mid-6th century. The railway line built in 1909 between Krems and Emmersdorf is a topographical marvel. Other settlements of note in the Wachau valley include Aggsbach, Bachamsdorf, Bergern im Dunkelsteinerwald, Furth bei Göttweig, Joching, Maria Laach am Jauerling, Mautern an der Donau, Mühldorf, Oberamsdorf, Oberloiben, Rossatz-Arnsdorf, Ruhrsdorf, Schwallenbach, Schönbühel-Aggsbach, Unterloiben and Willendorf.