Sargassum seaweed fills the shore where fishermen push their boat to sea in Playa del Carmen, Mexico, Wednesday, May 8, 2019. As the new normal, it may mark the highest-profile climate-change even yet, outpacing the bleaching of Australia's Great Barrier Reef or melting polar ice, just because so many more people visit the Mayan Riviera. (AP Photo/Victor Ruiz )

Tourists looking for sun and sand in Mexican resorts like Cancun, Playa del Carmen and Tulum have been disgusted by foul-smelling mounds of sargassum—a seaweed-like algae—piling up on beaches and turning turquoise waters brown, and experts are warning that it may be the new normal.

Mexico's Riviera Maya Caribbean coast provides half the country's tourism revenues and very little sargassum reached it prior to 2014. But a possible combination of climate change, pollution from fertilizers and ocean flows and currents carrying the algae mats to the Caribbean has caused the problem to explode.

While it may not have the global impact of melting of polar ice, the vast mats of sargassum filling the Caribbean could be one of the more visible climate-change events because of the sheer number of people who visit the region's popular tourist beaches, some officials say.

"This is one of the biggest challenges that climate change has caused for the world," said the government of Mexico's resort-studded coastal state of Quintana Roo. "This challenge requires a joint, multinational effort and a global commitment."

While tourist arrivals at the Cancun airport were up 3.3% in March over the same month last year, many fear this will not last long with the sargassum befouling white sand beaches and blue waters, as well as the air—sargassum decomposes with a rotten egg smell. As it decays and sinks to the bottom, it can also smother the coral the Caribbean is known for, and accumulations on beaches can make it harder for sea turtles to nest.

Sargassum seaweed covers the beach in Playa del Carmen, Mexico, Wednesday, May 8, 2019. Experts say the presence of sargassum seaweed is the new normal and residents are going to have get used to it. (AP Photo/Victor Ruiz)

"In my humble opinion it's a disaster that will eventually cripple the tourism, the businesses and, sad to say, destroy the local economy," said Jef A. Gardner, a frequent visitor to Playa del Carmen from Knoxville, Tennessee. "This is a Caribbean problem on the east coast that goes from Cancun all the way past Ambergris Caye in Belize."

The concerns may not be hyperbole: the sargassum mats appear even worse along parts of Mexico's coast than they did last year. And the problem affects almost all the islands and mainland beaches in the Caribbean to an extent. The U.S. Gulf coast got hit in 2014 and the east coast of Florida is getting sargassum this year.

The algae flooding into the Caribbean is coming from an unexpected source: the tropical Atlantic waters beyond the mouth of the Amazon River.

Chuanmin Hu, a professor of oceanography at South Florida University's College of Marine Science, says the sargassum mats appear to be the result of increased nutrient flows and ocean water upwelling that brings nutrients up from the bottom. Prevailing ocean currents carry the algae into the Caribbean, where it can grow further.

Sargassum seaweed floats off the beach in Playa del Carmen, Mexico, Wednesday, May 8, 2019. While concepts about what to do with collected sargassum are springing up, some propose using it as an aggregate additive for bricks, but its usefulness as a fertilizer or animal feed is limited by the chemicals it contains, like salt, iodine and arsenic. (AP Photo/Victor Ruiz )

He says the cycle is not likely to stop anytime soon.

"Because of global climate change we may have increased upwelling, increased air deposition, or increased nutrient source from rivers, so all three may have increased the recent large amounts of sargassum," said Hu.

While he says additional research is needed before definitively linking it all to human activity, he pointed to evidence of "increased use of fertilizer and increased deforestation" as possible culprits, at least as far as the Amazon is concerned.

Warming ocean waters are likely to play only a minor role since the area—the tropical Atlantic and Caribbean—has always been pretty warm.

Tourist walk through sargassum seaweed to their boat in Playa del Carmen, Mexico, Wednesday, May 8, 2019. Mexicans fear that tourists may flee the stinking mounds that pile up on beaches and turn the once-turquoise water brown, threatening a coast that provides fully half of Mexico's tourism revenues. (AP Photo/Victor Ruiz)

Soldiers walk the beach covered with sargassum seaweed in Playa del Carmen, Mexico, Wednesday, May 8, 2019. The U.S. Gulf coast got hit in 2014 and the east coast of Florida is getting sargassum this year, but apparently from a different source. (AP Photo/Victor Ruiz)

Workers remove sargassum seaweed from the beach in Playa del Carmen, Mexico, Wednesday, May 8, 2019. Shoveling or bulldozing up sargassum once it washes up on shore is a herculean task, as it returns hours later. (AP Photo/Victor Ruiz)

A man walk between the sargassum towards his boat in Playa del Carmen, Mexico, Wednesday, May 8, 2019. The huge sargassum mats appear even worse along some parts of the coast than they were last year. (AP Photo/Victor Ruiz)

A woman walks on the beach where a bulldozer removes sargassum seaweed in Playa del Carmen, Mexico, Wednesday, May 8, 2019. Tourists, unfortunately, come to Mexico's Caribbean coast for the sun, white sand, snorkeling and turquoise water of the ocean; while there are a lot of other things to do on the coast, sparkling fresh-water sinkhole lakes known as cenotes, Mayan ruins, and jungle, the beach remains the prize attraction, around which almost all the tourism infrastructure is centered. And tourists are unlikely to accept brown, algae-filled water. (AP Photo/Victor Ruiz)

Sargassum seaweed covers the beach in Playa del Carmen, Mexico, Wednesday, May 8, 2019. Strangely, for the moment, even after what looks to be the start of another bad sargassum year, local officials say there has yet to be any noticeable drop-off in tourism bookings. (AP Photo/Victor Ruiz)

A couple sleeps on the sand on the beach where sargassum seaweed is present in Playa del Carmen, Mexico, at sunrise Wednesday, May 8, 2019. Tourists arrivals at the Cancun airport were actually up 3.3 percent in March over the same month last year. But nobody thinks that can last for long with sargassum. (AP Photo/Victor Ruiz)

Meanwhile, business owners in Mexico's glitzy beach resorts are desperate for solutions.

"What you have to do is stop it before it even reaches the beaches," said Adrian Lopez, the president of Quintana Roo's employers' federation.

Contention lines of floating plastic booms can be anchored offshore to catch the incoming mats of algae, but as Lopez notes, some resorts have very shallow coral reefs located right offshore so the booms would be less of a solution.

And Hu warns that such a solution would be expensive. The tons of sargassum building up behind the booms has to be gathered up, put aboard boats and taken away in what would amount to hundreds of trips every day.

A worker pauses from removing sargassum seaweed from the shore of Playa del Carmen, Mexico, Wednesday, May 8, 2019. The problem affects almost all the islands and mainland beaches in the Caribbean. (AP Photo/Victor Ruiz)

Scientists have set up sargassum tracking systems that detect the amount of algae heading for shores in the Caribbean, but it's hard to predict when or where it will land.

Extracting it at sea risks the species that use the floating mats as cover for their young. But shoveling or bulldozing up sargassum once it washes up on shore is also a herculean task that can put at risk sea turtles' nesting sites.

"You can clean up a beach, get it clean, imagine starting at 6 a.m. and by 11 a.m. you don't have any algae, and by 7 p.m. when the sun sets, it's full again," said Lopez.

This all makes people nostalgic for the days before 2014 when sargassum "was very little, very manageable, not a problem, not a risk, just barely a line" in the sand.

Sargassum seaweed covers the beach in Playa del Carmen, Mexico, Wednesday, May 8, 2019. Local hotel owners and tourism industry workers, which is just about everybody, to some extent, in Quintana Roo, are feeling angry and abandoned by the federal government. (AP Photo/Victor Ruiz)

Now, some novel ideas for what to do with collected sargassum are springing up, such as using it as an additive for making bricks. But its usefulness as a fertilizer or animal feed is limited by the chemicals it contains, like salt, iodine and arsenic.

Tourists come to Mexico's Caribbean coast for the sun, sand, snorkeling and turquoise waters. While there are other things to do on the coast, like visiting sinkhole lakes known as cenotes, Mayan ruins and the jungle, the beach remains the prize attraction. And tourists are unlikely to accept brown, algae-filled water.

Local hotel owners and tourism industry workers—which is just about everybody to some extent in Quintana Roo—are feeling abandoned by the federal government, which is planning a fancy tourist train to connect the coast with Mayan ruin sites inland.

"With Sargassum, there is No Mayan Train," said a slogan launched by local businesses.

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