For much of its course from the Black Forest to the Black Sea, the Danube is constricted between concrete walls or uniform stone banks, flowing through some 60 power stations and busy docks.
But down here, for the last few hundred miles before it splays out into a vast delta, much of the river is as nature designed it _ broad, lazy, broken up with shoals and islands where pelicans nest, its banks anchored by weeping willows that drip water even on sunny days.
The Danube is a watery thread 2,857 kilometers (1,775 miles) long that binds the diverse peoples of 19 nations sharing its basin, weaving together economies and cultures from the richest nations of Europe to the poorest.
This month, European leaders are set to adopt a euro100 billion euro ($140 billion) Danube strategy to deepen those ties and improve the lives of 100 million people with faster transportation, cleaner water, less pollution and enhanced protection for wetlands and flood plains.
But it also envisions altering the Lower Danube to accommodate year-round navigation. Environmentalists warn this may have an irreparable impact on bird life, threaten the last breeding grounds for the majestic Danube sturgeon, and bring more polluting waterborne traffic to the Danube Delta, the largest wilderness remaining in Europe south of Scandinavia.
The Danube Strategy highlights the trade-offs needed to protect nature while advancing development, particularly among eastern European nations still lagging far behind Western living standards 20 years after the collapse of communist rule.
Europe's 37,000 kilometers (23,000 miles) of waterways are seen as cost-effective, environmentally friendly thoroughfares for moving goods across the highly industrialized continent _ cheaper, cleaner and quieter than rail or road.
A single cargo boat can carry the freight of 70 trucks, and a convoy of barges of coal, grain or other dry goods can move hundreds of truckloads without the road congestion or carbon-laden exhaust of heavy vehicles.
The plan foresees doubling the number of ships and barges plying the river, said Ton van Lierop, European Commission spokesman for regional policy. "Less than 10 percent of shipping capacity of the Danube is being used."
But defenders of the Danube worry about exposing the pristine delta to so much new traffic on top of an existing 4,000 boat fleet, much of it 50 years old, prone to oil leaks, pollution, occasional collisions and the careless discarding of rubbish.
Environmentalists agree water transport emits far less carbon and other pollutants than bumper-to-bumper trucks on narrow two-lane roads. But they worry about damage to the river as engineers use dredgers and concrete to eliminate the choke points blocking navigation for up to two months when the water is low.
"We cannot oppose this evolution. The key is how you do these things," said Orieta Hulea, a biologist for the Worldwide Fund for Nature, or WWF. It's a question of "balancing nature against human interest."
The blueprint has been years in the making. Conservationists derailed shippers' early proposals to turn the Danube into a navigational superhighway deep enough for oceangoing vessels. Environmental protection is now enshrined as a pillar of the strategy.
Planners say they have done all they can to incorporate environmental concerns.
"This is a new planning approach, quite different from the 20th century and the end of the 19th century" when the upper river was straightened, dredged and radically modified, said Markus Simoner, of Via Donau, the Austrian water management company that coordinated part of the project.
"We should not work against nature, but with nature," he said from his Vienna office, with a distant view of the river.
That means keeping human intervention to a minimum. Rather than deepen channels, ships would rely on real-time sonar and electronic monitoring to map out safe routes through the shifting riverbeds. Some dikes would be removed to reopen floodplains and restore wetlands that dried up decades ago. On the Lower Danube, deep-draught ships would give way to shallow barge convoys powered by snub-prowed push-boats.
"The Danube is not just a waterway," Simoner said. It also is a source of energy, drinking water, recreation and a means of flood and sewage control. "There cannot be one-sided solutions ... or one-dimensional thinking."
The opening of a canal linking the Danube to the Main and Rhine rivers in 1992 created a shipping route from the North Sea to the Black Sea. Cargo from distant ports passes through dozens of locks to reach Vienna, Bratislava, and Budapest. At the Iron Gates gorge, two dams between Romania and Serbia control a plunge of more than 40 meters (130 feet). After that the river meanders gently through its final 535 miles (860 kilometers).
The Lower Danube is a treasure of biodiversity. The delta alone, which has just 10,000 people living in its 580,000 hectares (1.4 million acres) of marshland, hosts 320 bird species, 2,000 different animals and 4,500 types of plants.
Still, the human footprint already is heavy. Bits of plastic cling to tree branches when water levels drop, and garbage marks the campsites of sports fishermen. Speedboats _ some driven by poachers violating the ban on commercial fishing _ zip through the delta's channels.
An increase in river traffic would yield a spin-off effect of investment in new industries, new services, and bigger ports, said Van Lierop, the European Commission official, interviewed in his Brussels office. An integrated transport plan will lead to upgraded railways and better roads in a country like Romania, which now has only a few dozen miles (kilometers) of European-standard highways.
The Economic Commission for Europe says water transport accounts for less than 6 percent of the movement of goods, while 76 percent goes by road and 18 percent by rail. The Hungarian EU presidency, in a paper published in April, urged a migration of more freight to inland waterways.
The strategy that goes before the European Council in June is long on general aspirations but short on specific targets. Among its time-bound objectives are bringing internet access to everyone within two years, restoring nutrient pollution flowing into the Black Sea to 1960 levels by 2020, and developing a series of port-to-land transport terminals by the end of the decade.
It also promises to bolster national parks, promote the culture of the Roma, or Gypsies, and to prepare a fortress-lined Roman road parallel to the river as a World Heritage Site.
Some 80 projects are roughly sketched in the plan. Financing will come from existing EU budgets, mainly the European Regional Development Fund, said Van Lierop.