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.
Kladovo
Though the river Danube is very polluted by international standards, many people still fish in it. Before the power plant was built, sturgeon caviar from this area was very popular and was exported as a delicacy to the western Europe and the United States. In the 1960s, up to 3 tons of caviar yearly was exported from Kladovo. Record catch from that period is a heavy sturgeon with of the roe in it. However, the records from the past, dated in 1793, report of the sturgeon which had . The specificity of the Kladovo's caviar was that the roe gets "ripe" enough during the long journey of the fish from the Black Sea upstream the Danube. Also, roe was turned into the caviar using the dry method.