5,000-mile seaweed belt heading toward Florida

A 5,000-mile seaweed belt lurking in the Atlantic Ocean is expected in the next few months to wash onto beaches in the Caribbean Sea, South Florida, and the Yucatán Peninsula in Mexico.

The Great Atlantic Sargassum Belt — as the biomass stretching from West Africa to the Gulf of Mexico is called — contains scattered patches of seaweed on the open sea, rather than one continuous blob of sargassum. It’s not a new occurrence, but satellite images captured in February showed an earlier start than usual for such a large accumulation in the open ocean.

Once it washes ashore, sargassum is a nuisance — a thick, brown algae that carpets beaches, releasing a pungent smell as it decays and ensnares humans and animals who step into it. For hotels and resorts, clearing the stuff off beaches can amount to a round-the-clock operation.

Sargassum originates in a vast stretch of the Atlantic Ocean called the Sargasso Sea, which lies well off the southeast U.S. The Sargasso has no land boundaries; instead, four prevailing ocean currents form its boundaries.

The matted brown seaweed stretches for miles across the ocean and provides breeding ground, food and habitat for fish, sea turtles and marine birds, according to the National Oceanic and Atmospheric Administration.

“It’s a dynamic, constantly changing set of pieces of this large mass,” said Rick Lumpkin, director of the Physical Oceanography Division at NOAA. “It’s not one big continuous blob heading straight to South Florida.”

In recent years, sargassum has carpeted beaches on some Caribbean islands and Mexico’s Yucatán Peninsula in the spring and summer months. Beach towns and cities and hotels have struggled to keep up with the huge amounts of seaweed that wash ashore.

Some sargassum has already reached beaches in Key West, said Chuanmin Hu, a professor of oceanography at the University of South Florida. But most of it will arrive in the summer, Hu said.

“What is unusual this year compared to previous years is it started early,” Hu said. The algae generally blooms in the spring and summer, but “this year, in the winter, we already have a lot.”

Scientists estimate there’s more than 10 million metric tons of sargassum in the belt this year. Lumpkin called it “one of the strongest years, but not the strongest” since scientists began closely observing the biomass via satellite imagery in 2011. 




Seaweed covers the Atlantic shore in Frigate Bay, St. Kitts and Nevis, Aug. 3, 2022. On shore, sargassum is a nuisance — carpeting beaches and releasing a pungent smell as it decays. For hotels and resorts, clearing the stuff off beaches can amount to a round-the-clock operation. (AP Photo/Ricardo Mazalan, File)