Fence posts mark what was once the edge of Lake Koroneia, now several metres from the shore. Greece's fourth-largest lake, near Thessaloniki, used to extend over 45 sq km. In 30 years it has lost a third of its surface area, its depth has shrunk from five metres to only one, sometimes less. In summer 2009 you could walk across. In the heart of Europe a lake is dying.

There is a tip beside one of the fence posts, with an old television, broken furniture and bin liners. Yet this place belongs to the Natura 2000 scheme, a European network of natural heritage sites. It also benefits from the protection of the Ramsar convention on wetlands. "We organise regular drives to clean up the area, but there is always more rubbish," says Marios Asteriou, from the organisation responsible for this lake and another nearby.

The European commission finally lost its patience on 27 January and lodged a complaint against Greece for its failure to protect the lake. Brussels also claims that the government has failed to comply with European directives on birds and the natural habitat, and on the treatment of waste water.

In 2004 Brussels gave the go-ahead for plans to restore the lake, having agreed to fund three-quarters of the work with a $27m grant. Seven years later only a quarter of the work has been completed. The project depends on four different ministries and the regional police chief, making management all the more difficult.

Lake Koroneia is surrounded by farmland and in the 1980s it suffered from increasingly intensive agriculture, but also from the growth of industry. Factories emptied waste water into the lake. The waste water from the neighbouring town of Lagadas also comes here. The sewage plant, built in 2001, has still not been connected to the drainage system.

For the time being Koroneia is a pretend lake. It looks like one, with a vast expanse of water ringed by reeds, but, "it is no longer a lake", says Maria Moustaka, a biologist at Thessaloniki University. She says it is more like a culture fluid in which toxin- resistant algae and microbes flourish.

This article originally appeared in Le Monde