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.
Transport in Germany
Waterways: 7,467 km (2013); major rivers include the Rhine and Elbe; Kiel Canal is an important connection between the Baltic Sea and North Sea and one of the busiest waterways in the world, the Rhine-Main-Danube Canal links Rotterdam on the North Sea with the Black Sea. It passes through the highest point reachable by ocean-going vessels from the sea. The Canal has gained importance for leisure cruises in addition to cargo traffic.