Just as France's holiday season reaches its peak, the carcasses of wild boars are appearing on Brittany's celebrated coastline, raising fear that a potentially lethal algae is at work that could threaten the health of humans as well.
The bodies of more than 30 of the animals have been found in the sea or on the slimy, seaweed-covered beaches around the bay of Saint Brieuc, where some coastal areas have been sealed off.
Environmentalists believe the potentially fatal algae is the result of a buildup of nitrates from fertilizers used by the region's farmers, many of whom raise pigs, seeping into the sea.
July and August are the busiest months for France's seaside resorts as the country's schools close for vacation. This year, tourists and holidaymakers expected along the country's Atlantic coast had already been discouraged by unseasonal rain and high winds.
Now the Breton region known as the Cotes d'Armor has taken a second hit with the rise in green algae contamination that has led to several beach closures and unwelcome headlines about "killer" seaweed.
On Tuesday, 18 dead boars were found in the Saint Brieuc bay. The day after, three more were discovered on the muddy banks of the nearby Gouessant estuary at Morieux. Another boar carcass was found Thursday in the area, bringing the number of dead animals this month to 34.
Algae is a generic term covering anything from microscopic organisms to seaweed. The kind of algae causing problems along the Brittany coast is known scientifically as Ulva, but is often called sea lettuce. It has been present along the rugged north Breton coastline for decades, but levels of contamination have increased in recent years.
After the kind of heavy rain the region has been suffering, fertilizers containing nitrates from farmland and waste material from livestock can be washed into streams and rivers that flow into the sea, boosting the growth of algae.
Scientists say that when the weed, in itself harmless, is washed onto the beach, the surface dries in the sun, forming a hard crust under which hydrogen sulfide, a foul-smelling and poisonous gas, is trapped. When the surface is broken, the gas, with its characteristic smell of rotten eggs, is released.
In 2009 a 27-year-old horse rider fell unconscious and his horse collapsed after slipping on the algae on a beach at Hillion in Brittany. The animal was believed to have died after inhaling gas released by the weed. The rider, a local veterinarian, was rescued from a yard-high pile of rotting algae.
An inquiry is still underway in the death of a man who suffered a heart attack while transporting rotten seaweed in a truck in 2009.
Gilles Huet, a member of an association dedicated to preserving the coast and waterways of Brittany, said the exact reason for the boars' deaths was unknown. He said, however, that the coincidental rise in green algae in the Saint Brieuc bay and death of the boars was troubling.
"One of the theories we have is that the animals might have drunk water that contained algae," he told the Agence France-Presse news agency.
Poice officer Philippe De Gestas said necropsies were being conducted on the dead animals. Experts were testing for hydrogen sulfide, he said, and they "could not exclude that seaweed was to blame."
"The animals were not sick and they did not drown," De Gestas said.
An official analysis of the water in the estuary found that green algae were "above the alert level but below the danger level."
The French government has launched a long-term program to clear the beaches of algae using bulldozers. Thousands of tons of green algae have been cleared from the Breton coast this year. However, environmental campaigners say this is a short-term solution and that nothing will change unless farmers cut down on the use of nitrate-based fertilizers.
On a visit to Brittany this month, French President Nicolas Sarkozy, who is facing a reelection battle, defended the farmers and called those who criticize the use of nitrates "environmental fundamentalists."
The agricultural lobby is one of the most powerful in France.
Willsher is a special correspondent.