The 1,770-mile Danube is a player in, and a witness to, the conflicts that have divided the peoples along its banks. During the Balkans wars the murky waters are alleged to have provided Slobodan Milosevic's henchmen with a natural dump for scores of murdered civilians. The conflict, international sanctions and Nato's 1999 bombing of Yugoslav bridges dealt a devastating blow to the shipping industry downstream.
Now, the Danube's countries are seeking to turn the tide. Austria's Foreign Minister, Benita Ferrero-Waldner, launched the Danube Co-operation Process yesterday. The EU-backed initiative aims to promote trade, traffic and tourism along Europe's second-longest river.
Chris Patten, the EU's external affairs commissioner, pointed to the historic geo-strategic role of the river in the development of its peoples, saying: "I think we need to make the most of that as Europe consolidates the advances of the last few years."
Edgar Martin of the British-based consultancy Danube Research said: "If you sit in a café in Frankfurt and watch the ships go up and down [the Main], there's always something going on. In Romania you could sit for hours on some days before you see a vessel moving."
The river was declared open again last November, but at Novi Sad in Serbia work on a new bridge has not begun and a temporary pontoon bridge opens only three times a week and charges ships to pass.
Erhard Busek, the co-ordinator of the EU's Stability Pact for South-Eastern Europe, said: "Sometimes I have the feeling they're very pleased to earn a lot of money by opening the bridge."
Travel west and the war wounds give way to pollution. Fishermen on the Tisza tributary say their catch is a third of what it was before a cyanide spill at Romania's Baia Mare goldmine two years ago.
Further upstream again lies evidence of a dispute between Hungary and Slovakia. In 1989 Hungary suspended work on a joint dam complex with Czechoslovakia. The case went to court, but the 1997 ruling seemed only to confirm both the Slovakian view that the Nagymaros dam in Hungary should be built and the Hungarian position that Slovakia's Gabcikovo dam should be dismantled.
After passing Johann Strauss's hometown of Vienna, the river winds its way through the Wachau wine region. At this point the Danube, if not exactly blue, best fulfils the promises of his waltz. From there it is a few hundred more miles to the source in Bavaria, generally considered to be at Donaueschingen, although not everyone agrees.