When Sweden scuttled 20 huge wooden warships more than 250 years ago, it was seen as a desperate measure to block the enemy Danish fleet. Now those same wrecks could scuttle the key component of a European energy plan - the construction of a 1,200km (746-mile) gas pipeline along the cluttered floor of the Baltic Sea.

Russia and Germany are building the pipeline to avoid the political problems of transporting gas overland - Ukraine and Belarus, in the midst of price rows with the energy supplier Gazprom, have threatened to interrupt supplies to Western Europe.

The seabed route, known as Nord Stream, is turning into an obstacle course of a different kind. Not only do 100,000 tonnes of unexploded Second World War munition lie scattered along the route, but the German Navy is concerned that one of its live shells might hit the pipeline and set off an explosion during Baltic exercises.

Meanwhile, ecologists are protesting at the disruption to fish breeding grounds and the Swedes fear that Russian submarines guarding the pipeline might spy - as they have done in the past - in their waters.

Then there are the shipwrecks. In 1715 the Swedes filled 20 of their largest vessels with stones, sailed them southeast of the island of Rügen, which now belongs to Germany, and sank them. The result was a chain of jagged boobytraps more than a kilometre long, that served as a frontline defence against the Danes.

The wrecks were discovered in 1990 and declared to be a valuable maritime archaelogical site. This is precisely the spot where the Nord Stream pipeline is supposed to rise and come on land. The gas pumped from Vyborg in Russia, close to the Finnish border, will be pumped under high pressure until it reaches Greifswald, close to Rügen.

“We're going to send divers down to the wrecks in the coming weeks,” said Jens Lange, who is in charge of gaining planning permission for the pipeline in German waters. “I'm expecting to recover one of the wrecks next year.”

His plan is to make a hole in the tight chain of shipwrecks and allow space for the pipeline to run past.

The operation is not as straightforward as it sounds. Removing one out of twenty ships could destabilise the whole rotting fleet. And the construction work on the pipeline could lead to their disintegration.

The operation will be paid for by the Russo-German consortium, half owned by Gazprom, which is aiming to complete the pipeline in 2011. This deadline appears to many experts to be unrealistic because the seabed of the Baltic has been poorly charted. The pipeline is supposed to run past the Swedish island of Gotland, where about 100 wrecks have been found. Historical sources indicate that 2,500 ships have sunk around the island in the past 250 years.

Some experts calculate that the gas will begin to flow only in 2015. Every month of delay pushes up the costs. The price of steel, for example, has been rising steeply, which will push up the cost of producing more than 1,000km of pipeline.

Nord Stream has estimated that the EU demand for gas will be a third higher by 2015. The question is whether the price of Baltic gas will be competitive enough by the time the pipeline has been built.

The Finns, the Swedes, the Danes - the route of the pipeline has been shifted around the Danish island of Bornholm - the Poles and the Germans have all lodged complaints. No one seems to be in a hurry to give the go-ahead to a pipeline that extends the influence of Gazprom in the West.

“These are highly sensitive waters,” Andreas Carlgren, the Swedish Environment Minister, said. “We need as much information as we can get before we can approve such a huge project.”

Vital link with the West

— The first pipeline is expected to pump 27.5 billion cu m of gas a year from 2011. A second, parallel pipeline will double the capacity in 2012

— The scheme is estimated to cost ¤7.4 billion (£5.9 billion). Independent experts believe that it will cost ¤12 billion

— The gas arrives in Germany and will be transported to Britain, France, Denmark and the Benelux countries

— The deal for the pipeline was clinched in 2005 by Vladimir Putin, then President of Russia, and Gerhard Schröder, when he was German Chancellor

Times Recommends

• Riots as Zimbabwe turns off water supply
• Tourists told to stay away amid Venice floods
• Protest is no picnic for Carrefour customers