For 10 points, name this river originating in the Black Forest and passing through the capitals of Slovakia, Hungary, and Austria, the second-longest river in Europe.
Its tributaries include the Prut, Morava, and Sava, and it is formed by the confluence of the Brigach and Breg Rivers at Donaueschingen. A canal completed in 1992 connects this river to the Main River, allowing travel between the North and Black Seas. For 10 points, name this river originating in the Black Forest and passing through the capitals of Slovakia, Hungary, and Austria, the second-longest river in Europe.
Its tributaries include the Prut, Morava, and Sava, and it is formed by the confluence of the Brigach and Breg Rivers at Donaueschingen.
{Danube} River [or {Donau}; or {Dunaj}; or {Duna}; or {Dunav}; or {Dunarea}; or {Dunay}]