A record-breaking surge of brown, smelly seaweed is inundating Mexico's Caribbean coastline, leading to beach closures in premier tourist destinations and inflicting escalating economic damage on local hotels, restaurants, and shops.

This unprecedented mass of sargassum, a brown seaweed that traverses the Atlantic in vast mats before ocean currents push it towards Caribbean shores each spring, has prompted the federal government to devise an emergency response plan.

In the eastern state of Quintana Roo, a popular tourist hub renowned for its once-pristine beaches like Cancun and Playa del Carmen, environmental officials anticipate 119,000 tons of sargassum will wash ashore by year's end.

This figure significantly surpasses last year's record of 96,000 tons. Brian Barnes, a research assistant professor at the College of Marine Science at the University of South Florida who studies the phenomenon, attributes the increase to "warmer temperatures," noting that a combination of nutrients and extended periods of sunlight also contribute. Once stranded, sargassum rapidly decomposes, emitting a stench often likened to rotten eggs.

The economic fallout is severe. Tulum Councilman Eugenio Barbachano described the decline in tourism as "extremely serious," blaming the sargassum epidemic.

"The low season is not just low, it is critical," he stated. Workers are seen lining many beaches along Quintana Roo's Riviera Maya, knee-deep in seaweed, engaged in the seemingly Sisyphean task of shoveling heaps of sargassum off the shoreline, even as some of the season's worst months may still be ahead.

Quintana Roo Governor Mara Lezama has said managing sargassum costs the state roughly 11% of its GDP, or about $2 billion annually, while the Riviera Maya hotel association estimates the cost of combating the seaweed at roughly $150 million annually.

In recent weeks, dozens of Quintana Roo beaches have been placed on red alert for the algae, with some forced to close entirely. By late June, a local monitoring network reported that 92.5% of the state's beaches registered an "excessive" level of sargassum. "Quintana Roo is a state that sells beaches, blue sea and water activities," said Carlos Solis, a local tourism service provider. "It affects everything."

Beyond tourism, marine scientists warn that decomposing seaweed deprives underwater plant life of sunlight, diminishing biodiversity, and can even leach arsenic and other heavy metals into the sand. Workers who have previously cleared sargassum from beaches have reported itchy and burning skin, headaches, fatigue, and nausea, symptoms linked to the algae, according to a 2025 study published in a scientific journal.

In response, the Mexican Navy has deployed a sargassum-fighting fleet, including 11 specialized coastal ships, an amphibious sargassum collector, 18 support boats, two barges, and four drones. It has also installed over 9,000 meters (29,500 feet) of containment barriers to protect beaches.

The government is expected to unveil a revised response plan on July 30, hoping to better address the issue. Brian Lapointe, a research professor at Florida Atlantic University’s Harbor Branch Oceanographic Institute, suggests the Caribbean needs a system connecting "satellite observations and modeling forecasts with targeted intervention before sargassum reaches the beach."

Despite the challenges, some tourists are still venturing into the seaweed-blanketed waters. "I went swimming today," remarked Wendy, a Swedish tourist. "I expected worse."