It has been dubbed Europe's Amazon -- but yesterday any comparison with the tropical South American river seemed ridiculous.
Instead, the "Blue Danube", commemorated by Johann Strauss with a waltz of the same name, resembled the arctic, covered in a dense carpet of ice stretching for hundreds of miles.
Dynamite had to be used to blow apart ice floes in a desperate attempt to prevent catastrophic flooding.
The result is that hundreds of container barges that normally plough the length of the waterway have been confined to port. The authorities yesterday said that traffic from upstream Austria had come to a virtual standstill to its river's mouth on the Black Sea.
The culprit is the cold front that has plunged central and south-eastern Europe into a harsh and unexpected winter of near-Siberian proportions for nearly a fortnight.
Via Donau, the body responsible for co-ordinating traffic movement in all nine countries through which the 1,780-mile river flows, said: "For the Danube to freeze we need temperatures of under -10C for a week. That is currently the case."
With temperatures on the continent reaching a low of -33C, the Danube has emerged as one of the winter's major victims. Ice floes on the stretch of river that flows through the Serbian capital Belgrade are currently up to half-a-metre thick and all vessels seeking to pass along the country's 600km of waterway are harbour-bound.
Yesterday the Serbian authorities mobilised the country's armed forces to address the problem. Military experts were dynamiting the pack ice on some sections of the river due to fears that a quick thaw could bring about severe flooding.
"We need a slow thaw of around 5C so that the snow melts slowly and causes no bigger problems," said Aleksandar Prodanovic, a Serbian flood control expert.
In Croatia, an operation was mounted to rescue the crew of a barge trapped in the ice near the port of Vukovar since last Friday. The three men on board had run out of food.
And in Bulgaria, the authorities have banned navigation on the river. A total of 224 vessels are reported to be harbour-bound in six river ports.
The economic impact of the freeze has yet to be fully estimated, but it is certain to be significant.
The collapse of communism in most of the countries through which the mighty river flows has led to a substantial increase in its use as a trade route.
In 2010, 11.1 million tonnes of goods were transported via the Austrian section of the Danube alone. That was up by 1.7 million tonnes on the figure for 2009. (© Independent News Service)