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.
Budapest
The river Danube flows through Budapest on its way from Germany to the Black Sea. The river is easily navigable and so Budapest historically has a major commercial port at Csepel District and at New Pest District also. The Pest side is also a famous port place with international shipping ports for cargo and for passenger ships. In the summer months, a scheduled hydrofoil service operates on the Danube connecting the city to Vienna.