SAINT-LOUIS, Senegal — Houses on the shore seem to have been ripped open by a giant claw. The corner of an abandoned school is gutted, leaving what looks like a gigantic bite mark. All that is left of a nearby mosque is a flattened pile of concrete blocks and twisted iron rods.
The culprit behind this destruction in Saint-Louis, on the northern edge of Senegal’s Atlantic Coast, is not some mythical sea monster, but the ocean itself.
At a rate that is increasingly worrying to residents and officials, waves are lapping at buildings on the shoreline, pulling sand away and eroding foundations until walls collapse and floors cave in.
On a recent morning, Massamba Diaw, 70, showed a jumble of ruins in the sand.
“Two months ago, we were standing here, under a roof,” he said. Like most men in his neighborhood, Mr. Diaw was a fisherman. Like many of his neighbors’, his house is now crumbling.
“We all feel really sad, and threatened,” Mr. Diaw said, pulling his grandchildren away from the edge of his first floor, which is now exposed to wind and rain. “What will these kids do in the future?”
But the impact is particularly stark in Saint-Louis, especially on the Langue de Barbarie, or Barbary Tongue, a thin, sandy peninsula that extends over a dozen miles further south and acts as a natural buffer with the ocean.
“For the past decade, people here have really started to suffer the wrath of coastal erosion,” said Latyr Fall, the city’s deputy mayor for economic issues.
Saint-Louis, a city of over 232,000 that was first settled by the French in the 17th century, was the colonial capital of French West Africa until 1902.
It is split in two by the Senegal River, which snakes down from the north, forming a natural border with Mauritania. Eastward, on the mainland, is most of modern Saint-Louis. Westward is the Langue de Barbarie, which separates the river from the ocean until the two meet.
In the middle is an island best known to tourists for its preserved 19th-century colonial architecture — low, pastel-colored houses with vivid shutters and wrought-iron balconies, some renovated and turned into elegant guesthouses, others slowly crumbling but still graceful.
The island became a Unesco World Heritage site in 2000, and is host to cultural events like annual jazz and contemporary dance festivals. Erosion isn’t discussed much, said Staffan Martikainen, a Finn who runs an artistic residency program there.
“It’s surprising, in view of the fact that both the fisherman’s peninsula and the island might be gone in two generations, that real estate prices don’t go down,” he said.
But across the bridge that spans the small arm of the Senegal River, in the poorer neighborhoods on the Langue de Barbarie, coastal erosion is an immediate threat. About 80,000 people live there, on a stretch of land that is barely 600 feet wide in some places.
Crowds of children race the streets, jumping out of the way of horse-pulled carriages and sputtering minibuses. Green fishing nets lie tangled on the sidewalk while tethered goats munch on trash in sandy side alleys.
Many in these neighborhoods are from the Lebou ethnic group, traditionally a fishing community. The ocean might have destroyed their homes, but it was also a source of food, income and community.
“In Saint-Louis, if fishing thrives, everything thrives,” said Mr. Fall, the deputy mayor. “But if fishing hurts, then everything hurts.”
Fishing is now harder than ever for about 250 families that have lost their homes to erosion. Most of them — roughly 850 people — were resettled by the local authorities in a temporary camp several miles inland.
Abdou Gueye, 42, is one of them. His house was destroyed during a storm surge in August and his family was brought in October to the temporary settlement, a mix of small concrete houses and tents known as the Khar Yalla camp, in an empty field far from downtown.
It has several outdoor showers and toilets, and some outside lighting, but lacks proper access to water and to waste management, and it is prone to flooding.
Still, it is the distance to the coast that ails these fishermen the most.
“Now we have to pay for transportation to the ocean,” Mr. Gueye said, sitting under a pitched white tarp to avoid the sun. In the bustling fishing district, neighbors conveyed reports of a brewing storm, or of a good catch. “Now we are far away from all that information,” he added.
Nearby, Yaram Sène, 20, said leaving was on everybody’s mind. “There is nothing here, no police, no health facility, no school,” she said.
Mr. Gueye said each family had received about $900 from the authorities when their houses were destroyed, but nothing since. Few can afford to move elsewhere.
For those who still live on the Langue de Barbarie, Senegal is paying the French construction company Eiffage to build an embankment that shields houses from the ocean swell.
Made of giant five-ton bags of sand topped with rock-filled cages, it will run for about two miles down the coast until it reaches parts of an old colonial-era sea wall that are still standing.
But officials stress that the embankment is an emergency buffer to protect houses from immediate destruction, not a permanent fix for the erosion. Longer-term solutions have been proposed: building breakwaters or a new sea wall, resanding the beaches or clearing them to create a buffer zone.
The authorities are still waiting for results from continuing engineering studies to determine what to do. President Emmanuel Macron of France recently promised nearly $18 million to help, adding to existing funds from the World Bank.
Some, like 53-year-old Ahmet Diagne, are taking matters into their own hands.
Mr. Diagne used to live in Doun Baba Dièye, a village of fishermen, cattle breeders and farmers just south of Saint-Louis. But in 2003, scrambling to evacuate floodwaters swelling around the city, the Senegalese authorities hastily dug a channel in the Langue de Barbarie.
The breach quickly grew, bringing erosion to villages that had previously been shielded from it, and submerging Doun Baba Dièye. In 2009, residents started moving inland.
From his fishing boat, early on a recent morning, Mr. Diagne pointed to what was left of his former village: a few ruins on the shore, and a sunken tree covered with cormorants that used to be in the town square.
For the past several years, with financial help from the government and international organizations, he and his community have planted thousands of mangroves and pine trees known as filaos, to halt erosion and reclaim land then used to farm and sell cassava, cabbages, melons, sweet potatoes and other produce.
Mr. Diagne became a local expert of sorts on coastal erosion, even for those in Saint-Louis who had previously derided his warnings that they, too, would soon face his village’s fate.
“It was a bit hard for me in the beginning,” he said. “I received calls from people telling me: ‘Stop talking nonsense. You did not attend school. Who are you to talk about erosion and rising sea levels?’”
“But now,” he said, “people are calling me back.”