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.
EuroVelo
Running from Saint-Nazaire on the mouth of the River Loire along that river eastward through France, EV6 passes over the border to Switzerland to Lake Constance and then on to Tuttlingen in Germany, where it begins its way down the Danube following the (Danube Cycle Route). It follows that river, Europe's second longest, through Germany, Austria, Slovakia, Hungary, Serbia, Bulgaria and Romania to the river's mouth at the Danube Delta. It then continues southwards to end in Constanța, on the Black Sea.
EV7 runs from the North Cape to Malta, will whisk you from the Arctic Circle in Norway, the land of the midnight sun, to island hopping in the Mediterranean.