A diver swims beneath a mass of sargassum as rays a light pass between breaks in the mass.

A giant, rotting mass of seaweed threatens beach season in the U.S.

The 10-million-pound mass of floating seaweed—called the Great Atlantic Sargassum Belt—is washing up in Florida right as tourism peaks.

A diver swims beneath a mass of seaweed. Stretching some 5,000 miles across, the Great Atlantic Sargassum Belt can be an oasis for sea creatures—but a smelly nuisance for beachgoers through Florida and the Caribbean.
Photograph by DAVID DOUBILET, Nat Geo Image Collection

A 10 million-pound blob is riding ocean currents and washing up on the southern tip of Florida.

The Great Atlantic Sargassum Belt—a goopy mass of leafy, floating seaweed stretching across 5,000 miles—is slated to be a nuisance of record breaking proportions this year.

 In the past decade it's increasingly become a problem for beachgoers and seaside businesses—and a rotting, smelly one at that—but sargassum is a natural part of the ocean food chain.

“In the vast expanse of the ocean, it can be an oasis,” says Brian Barnes, a marine scientist at the University of South Florida. The patches of seaweed can be a home and source of food for passing fish and sea turtles. 

Here's what we know about where it came from—and

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