Danube
The Danube flows through many cities, including four national capitals (shown below in bold), more than any other river in the world. Ordered from the source to the mouth they are:
The Danube is navigable by ocean ships from the Black Sea to Brăila in Romania and by river ships to Kelheim, Bavaria, Germany; smaller craft can navigate further upstream to Ulm, Württemberg, Germany. About 60 of its tributaries are also navigable.
Inland Electronic Navigational Charts
As of November 2013, Inland ENC data conforming to the Inland ECDIS standard have been produced covering almost 10000 kilometers on European rivers/waterways including the: Rhine, Danube, Mosel, Neckar, Main, Scheldt, Garonne, Elbe, Sava and Drava Rivers and the Main-Danube Canal in Germany, the Netherlands, France, Belgium, Switzerland, Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Romania and the Ukraine.