Severe drought has hit Europe's second largest river, the Danube, turning it into a navigation nightmare for shipping companies all the way from Germany to Bulgaria.

According to Bulgaria's Danube exploration agency, the levels of one of the continent's most significant commercial waterways dropped to near-record lows in the past month, making it barely passable at several critical points.

"There is just no water! The situation is critical not only here on the lower Danube but also upriver in Hungary, Austria, Germany," Ivan Ivanov, deputy chief of Bulgarian River Shipping (BRP), told AFP.

"We load barges far below capacity. The navigable fairway is also so tight at some points that towboats can pass only if transporting one barge at a time instead of the usual six."

"Shipping costs are soaring, I don't even want to calculate our losses," he said.

Ports have also been operating at reduced capacity, and two ferry lines between Bulgaria and Romania were "on the edge" and would have to temporarily shut if water levels dropped another 50 centimetres (20 inches), Ivanov said.

Across the Danube in Romania, river administration authorities in the southeastern port of Galati noted that "intensive dredging activities are under way to assure the minimum depth levels" for navigation.

Bucharest also feared it would have to shut one unit of its sole nuclear power plant at Cernavoda if levels dropped further, as the reactor uses water from a Danube-Black Sea canal for cooling.

Such a shutdown already occurred in 2003 when the river level hit an all-time low, a record now less than half a metre away.

Meanwhile, Romania's state-owned Hidroelectrica company, 40 percent of whose production depends on the Danube, has said it is cutting electricity supplies.

With no rain clouds on the horizon, prospects for improvement were dim as experts forecast that water levels would drop even further or stagnate at best.

The water mark was already "below low-navigation level" along a 200-kilometre (120-mile) stretch of the Danube between Bezdan on the Serbian-Hungarian border and Pancevo, near Belgrade, Serbia's hydrometeorological service said.

Only lighter ships are allowed through, as media reported that around 100 freighters coming down the Danube were already blocked at Bezdan.

Port authorities in Croatia's main Danubian town of Vukovar banned navigation for ships with a depth of over 1.3 metres, citing insufficient water levels downstream in Serbia and Bulgaria.

Slovakia's State Navigation Administration meanwhile specifically ordered ships to load less cargo.

Merchandise transport on the upper Danube in Austria and Germany was also affected following what Austria's meteorological institute ZAMG said was the driest November since records began in 1858.

Cargo shipping on the Danube was only at 25 percent of the usual volume due to the low water levels, with cargo being diverted onto roads and rail, the Austrian waterway organisation Via Donau said.

The same was happening on the 69-kilometre stretch between the German ports of Straubing and Vilshofen -- the last free-flowing part of the Danube in Germany -- which has been completely blocked to cargo ships, with trains and trucks taking over, according to Adrian Bejan from Wuerzburg's Waterways and Shipping Directorate.

Shipping on the Rhine-Main-Danube canal linked to the North Sea also dropped severely over the past few weeks.

Meanwhile, the advance of winter is threatening a new obstacle.

"With no rainfall forecast anywhere from Germany down, the Danube's low and slow-flowing waters will freeze totally when temperatures drop low enough," BRP's Ivan Ivanov predicted.

The Bulgarian stretch of the Danube last froze in 1985.

Apart from being a key commercial waterway for Europe, the 2,860-kilometre river and its wetlands are home to unique ecosystems that have been severely damaged by human intervention such as gravel extraction, dredging and dam construction.

The environmental group WWF warned in a recent statement that the current drought was an important signal about the Danube's reduced ability to withstand extreme weather events.

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