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.
Rhine–Main–Danube Canal
The Rhine–Main–Danube Canal (German: "Rhein-Main-Donau-Kanal"; also called Main-Danube Canal, RMD Canal or Europa Canal), in Bavaria, Germany, connects the Main and the Danube rivers across the European Watershed, running from Bamberg via Nuremberg to Kelheim. The canal connects the North Sea and Atlantic Ocean to the Black Sea, providing a navigable artery between the Rhine delta (at Rotterdam in the Netherlands), and the Danube Delta in south-eastern Romania and south-western Ukraine (or Constanța, through the Danube–Black Sea Canal). The present canal was completed in 1992 and is long.