Behind the remains of washed-away fences, crumbling houses dot an expanse of the northern Senegalese coastline where a swollen river and an advancing sea are swallowing villages whole.

The fishing community of Goxu Mbath is one of many districts in the city of Saint Louis, the former colonial capital of French west Africa that, little by little, is disappearing under water.

"The waves surprised us at night. It was October 20. The water hit hard and knocked down walls," says Awa Sarr Fall, 68, outside her badly damaged oceanfront house.

"We are calling for the help of the state and we're willing to move elsewhere."

The village is on the Langue de Barbarie, a densely populated spit of land that is home to nearly 120,000 people.

Colourful dugout canoes are berthed on the sandy former peninsula, which protects the heart of the old colonial city from the Atlantic's fearsome breakers.

An archipelago in the mouth of the Senegal River often referred to as the "Venice of Africa", St Louis is anchored precariously between the fast-flowing currents of the swollen waterway and the ocean.

A 2008 UN-HABITAT report listed the city of 250,000, which is plagued by flooding during the rainy season when the river overflows, as the most vulnerable in Africa to rising sea levels.

The upheavals "are in part linked to climate change", but also "people have poorly designed their habitat space", says Pape Gombo Lo, a professor at Cheikh Anta Diop University in Dakar.

Named after Louis XIV, the UNESCO World Heritage site on the Mauritanian border was founded in 1659, becoming the first French settlement of l'Afrique Occidentale, trading in slaves.

Scientists say climate change is exacerbating the problem with increasingly heavy rain and a rise in the sea level.

On a visit to Senegal in 2014, the UN special representative on disaster risk, Margareta Wahlstrom, expressed concern for the fate of coastal and riverside towns, with some mayors telling her their villages spent 10 months out of 12 underwater.

"We want to move but we don't have the means. No authority has come to see us since the damage," says Abibatou Fall, another Goxu Mbath resident.

- Pessimism -

In 2003, heavy rain in the drainage basin of the Senegal River alarmed the authorities who, fearing flooding, dug a new channel for the river water across the Langue de Barbarie.

As the sea flooded into the river mouth the canal widened, from four metres at the outset to a gaping breach that is five kilometres (three miles) wide today.

"The forecasts are pessimistic for the Langue de Barbarie," says Balla Gueye, the city official in charge of the environment.

"The whole coast of St Louis is threatened," he said, adding that the city council had called on the state for help.

By way of response, the government recently announced a breakwater construction project that will cost one billion CFA francs ($1.6 million, 1.5 million euros).

The island community of Doune Baba Dieye, situated about ten minutes by motorised canoe from the mouth of the river, was the first casualty in St Louis.

"The water has engulfed the island and the people are gone," said the former village chief, Ameth Sene Diagne.

- Shipwrecked -

Diagne and his 800 neighbours had made their living from the precious mullet, sardines, bonga and tilapia that once thrived in the mangroves but disappeared after the salt water of the Atlantic began encroaching into the river.

Diagne, a father of 16 children from two wives, was the last to flee when the sea claimed his village in 2012.

"All this is due to the breach," says Diagne, one of the lucky ones who had enough money to build a new house further inland.

"We do not want it but in this country when you do not have a university degree, no one listens to you."

The nearby village of Keur Bernard was also deserted and others including Pilote Barre are threatened with extinction, according to experts.

The breach has also cost lives.

Fishermen who use the canal to go to sea are sometimes shipwrecked on sandbanks, says El Hadji Boubacar Dia, a local environmental official, estimating at nearly 200 the number of people killed since 2003.

Sea turtles and migratory birds are also at grave risk from the loss of habitat.

The results of a government study are expected by the end of the year "to see what to do with the breach, to close it or stabilise it," says Moussa Fall, head of the Langue de Barbarie national park.