MEXICO CITY >> Mexico has spent $17 million to remove over a half-million tons of sargassum seaweed from its Caribbean beaches, and the problem doesn’t seem likely to end any time soon, experts told an international conference today.

The floating mats of algae seldom reached the famed beaches around Cancun until 2011, but they’re now severely affecting tourism, with visitors often facing stinking mounds of rotting seaweed at the waterline.

Initial reports suggested the seaweed came from an area of the Atlantic off the northern coast of Brazil, near the mouth of the Amazon River. Increased nutrient flows from deforestation or fertilizer runoff could be feeding the algae bloom.

But experts like oceanographer Donald R. Johnson said, “Do not blame the Brazilians.” Johnson said it appears that other causes contribute, like nutrient flows from the Congo River.

Increased upwelling of nutrient-laden deeper ocean water in the tropical Atlantic and dust blowing in from Africa may also be playing a role, according to Johnson, a senior researcher at the University of Southern Mississippi Gulf Coast Research Laboratory.

While it sometimes appears sargassum mats float west into the Caribbean, experts say the seaweed actually appears to be sloshing back and forth between the Caribbean and Africa.

It all has the local population — which depends of tourism — fed up.

“Fighting sargassum is a chore every day,” said Cancun Mayor Mara Lezama. “You clean the beaches in the morning, and sometimes you clean them again in the afternoon or at night, and then you have to go back and clean it again.”

Ricardo del Valle, a business owner in the seaside resort of Playa del Carmen, said, “We offer sun and sand, nothing else. That is what we’re selling. And right now we’re fooling our tourists.”

Their anger increased this week when President Andres Manuel Lopez Obrador visited the coast and downplayed the seriousness of the problem. He recently said he would not contract out the work of cleaning up sargassum — or gathering it before it reaches shore — but will put the Mexican Navy in charge of building collector boats and cleaning the sea.

“I haven’t talked much about this, because I don’t see it as a very serious issue, as some claim it is,” Lopez Obrador said. “No, no, we’re going to solve it.”

Sargassum is not just a problem for Mexico; it affects, to a greater or lesser degree, all the islands in the Caribbean.

“We are seeing a major impact on our countries, economically, socially,” said June Soomer, the general secretary of the Association of Caribbean States, noting massive arrivals of seaweed “are now considered national emergencies” in some Caribbean counties like Barbados.

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