The wild horses of the Danube delta are a unique sight in Europe but conservationists warn that they are a threat to the region's forests and marshland

The port of Tulcea in Romania gradually drops out of sight as we sail down the Danube. It takes two hours to reach the little town of Sulina, at the southern extremity of the delta, where the river spills into the Black Sea. It feels as if we have reached the end of the world. Two thousand years ago the Roman empire chose this point as its eastern limit. More recently, in the 19th century, the European Commission of the Danube established its headquarters at Sulina.

But the fine buildings belong to another era. After the second world war communism put an end to hopes of development. "We did not even manage to build a little bridge across the river," complains Stefan Raileanu, a vet with a passion for the wild delta horses.

The horses are on the other side of the great river, in the undeveloped part of the delta. Some 4,000 roam freely here and over the years they have taken control of the well-protected wilderness. In 1991, the Danube delta was added to the Unesco World Heritage list. With hundreds of lakes and ponds, thousands of channels, huge stretches of forest and reed beds, the delta is a refuge for thousands of migrating birds and home to unique plant life.

But the horses have become a source of controversy. "If the horses settle somewhere the next day the place looks like a football pitch after two successive matches in the rain," says Vioral Rosca, the head of Macin natural park. "They are so destructive. There are flower species that are disappearing after taking ages to take hold. Soon this unique forest will be no more than a memory. To protect the delta they really have to go."

The Danube Delta National Institute (DDNI) sees things differently. "We need to find a solution to avoid stopping this new trend on the delta," says Romulus Stiuca, head of the institute. But due to a lack of resources local authorities have failed to restrict the horses to specific areas.

The story behind the wild horses goes back to the fall of the communist regime and the subsequent collapse of the nation's economy. With nothing left to feed their horses, farmers on the delta set them loose in the woods and they gradually returned to the wild. Occasionally the farmers would organise hunts, selling the carcasses to Italian companies. But the trade stopped in 2008 when vets realised the horses were suffering from infectious anaemia. By a strange twist of fate the disease saved their lives.

The fisherman in the village of Letea display little concern for the horses, though they do agree on their usefulness. "Round here, if you don't have a boat and a horse, you're not a man," says Vladimir Nistor, an old fisherman. "But the wild horses can go to the devil! I reckon they should all be slaughtered. They're destroying our forests." The village children disagree. Horse-riding is still an essential part of local culture and there are plenty of people who can ride bareback with an ease now seen only in Mongolia.

But wild horses are hard to catch. Mainly located in marshland, they race off when humans appear. Raileanu, who has been watching them for years, has learned how to get close. He walks for hours in the marshes, often with water up to his chest. It is exhausting work but well worth it. "Look at that. It's a unique sight in Europe. The population has deserted the villages, moving away to the towns, and the horses are gradually taking their place," he murmurs, having just found a group of several hundred animals.

He stands motionless in the water, hiding behind the reeds, watching the horses, which seem to have been there since the dawn of time. "They refuse to be captured and would rather die than give up their freedom," Raileanu warns.

In the midst of the Danube delta horses are still holding their own against humans.

This article originally appeared in Le Monde