A dug-out canoe speeds along the water then slows down suddenly before stopping altogether. Blocking its path are water hyacinths as far as the eye can see.

It's become a common occurrence in the last 20 years on Lake Nokou� in the south of Benin, which is fed by the fresh waters of the S� river and feeds into the Atlantic Ocean.

The aquatic plant, which is native to the Amazon basin in South America, was introduced to east Africa at the end of the 19th century and is now found across the continent.

On Lake Nokou�, as elsewhere around Africa, the proliferation of water hyacinths disrupts fishing, the transportation of goods and people, and contributes to the spread of malaria.

"Water hyacinths are a paradox," said Fohla Mouftaou, a Belgian-Beninese paediatrician who runs the firm Green Keeper Africa (GKA).

"In enough quantities they filter water and are a carbon sink. But too much of them and they begin decomposing and letting off greenhouse gases.

"By doing something that allows the balance to be restored you only keep the benefits."

Restoring the balance and using the surplus of water hyacinths in an economically viable and sustainable way is what Mouftaou and two associates have been doing for the last two years.

- Fertilisers and fibre -

A bio-refinery set up on a peninsula near the lakeside village of S�-Ava is the centre of the company's operations.

S�-Ava gives its name to a municipality incorporating several villages on stilts, which is home to some 100,000 people, most of them fishermen.

On the ground is a carpet of dried water hyacinths. Under a long roof, more plants are piled up in a composter.

"We currently have seven tonnes," said David Gnonlonfoun, a French-Beninese public works specialist who has lived in Benin for the last 15 years.

"We started work in March and in 2015 we harvested 500 tonnes."

In a warehouse, four workers transform the raw material with the help of a home-made crusher, without adding chemicals.

The dried plant is turned into organic fertilisers, animal feed and a fibre that absorbs oils and hydrocarbons, making it an effective tool in the clean-up of industrial sites.

The company has set up a partnership with a Mexican firm, Tema, which it has developed and successfully commercialised the fibre. Pemex, the state-run Mexican oil firm, is among its users.

About a dozen women from S�-Ava are responsible for collecting water hyacinths and drying them on the banks of Lake Nokou�.

The jute sacks they fill and deliver earn them 200 CFA francs (about 30 euro cents, 32 US cents) for 10 kilograms (22 pounds).

"In our language we call the hyacinth 't�gbl�', which means the land is ruined. Now we say 'tognon', the land is good," joked one local woman, Rosaline Adanhou.

From the window of his office, the deputy mayor of S�-Ava watches the women work.

"It's as if we've found our saviour," said Andr� Todje. "The hyacinth was a scourge, now it's a resource."

- Fully fledged business -

Mouftaou said it took some effort at first to convince the local people that Green Keeper Africa wasn't a non-governmental association but a fully fledged business.

Three associates stumped up 3.0 million CFA francs to get the firm off the ground and it has since received technical and financial support of a Fair Trade financier SENS-Benin.

It sells the absorbant fibre for 12,000 CFA francs per 10kg.

"We're interested to see this here in Benin," said the head of one oil firm, who asked to remain anonymous.

"We use it for leaks and when lorries are loaded. It's very effective."

In powder form, hyacinths can absorb oil spills, which potentially makes tiny Benin's neighbour Nigeria -- Africa's number one oil producer -- a key market for development.

Other uses not yet exploited include using the fibre for sanitary towels, which are either not readily available or too expensive for many African women.

For Gnonlonfoun, the business means the lake's waters can be cleaned and a useful product recovered.

The company is currently in talks with a cement producer to use used fibre from oil spills as fuel for its ovens, he added.

"It's come full circle," he said.