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Photos show seaweed 'blob' washing ashore in Florida

The giant mass of sargassum is expected to continue to grow and peak this summer, dumping huge amounts of stinky, smelly seaweed on some Florida beaches as it decomposes.

Two people stand on beach between lapping wave and a huge pile of seaweed.
Beachgoers walk past seaweed that washed ashore on Thursday in Fort Lauderdale, Fla. (Joe Raedle/Getty Images)

A giant "blob" of sargassum seaweed measuring 5,000 miles wide — twice the width of the continental United States — is headed for the Florida coast and already covering beaches with algae that will begin to smell as it decomposes.

Sargassum is a type of seaweed algae that floats in island-like masses without ever attaching to the seafloor. According to the National Oceanic and Atmospheric Administration, it functions as a floating habitat providing food, shelter and breeding grounds for many different types of sea animals.

Chuanmin Hu, a professor of optical oceanography with the University of South Florida, said the mass of seaweed, or “mat,” making its way toward Florida is not so much a “blob” but more of an “elongated belt.”

“There is not a single source, but sargassum is a natural plant in the Atlantic Ocean so it can grow in the entire tropical Atlantic,” Hu explained in an email to Yahoo News.

"Most beaches on the west coast of Florida will be spared but some beaches on the east coast will receive Sargassum of variable amount."

In this aerial view, several dozen beachgoers frolic among piles of seaweed on a beach.
More seaweed on a beach in Fort Lauderdale, Thursday. (Joe Raedle/Getty Images)

Once the seaweed begins to rot, it releases a substance called hydrogen sulfide, which gives off an unpleasant odor similar to rotting eggs. While it may be smelly, for the most part sargassum isn’t a health hazard or unsafe for humans — though those with respiratory problems should steer clear.

“Only when too much of the seaweed gets decomposed on the beach or in nearshore waters, then does it become a nuisance for animals and humans. People with respiratory problems don’t want to get close to the rotten, smelly seaweed. But it is not toxic in the ocean,” Hu said.

“For small amounts (e.g., a mat like the size of a room), you can swim around. But for large mats such as a football field, you want to avoid it,” he added.

Florida’s seaweed season runs from March through October, though an expert told the New York Times that this year may be the “biggest year yet on record.” So while sargassum’s presence on beaches should eventually peak and decline, it will inevitably return.

“It will continue to grow until June/July, and then start to decrease until winter. Then next year it will enter another cycle,” Hu said.

A satellite map of the earth oriented to show Florida and the Atlantic Ocean.
A satellite map dated March 8-14 shows the "elongated belt" of sargassum seaweed. (USF Optical Oceanography Lab/Google Earth)

But while it may be annoying for beachgoers, rather than disposing of all that seaweed some of it may serve a higher purpose. A local Palm Beach County TV station reported that many cities hire firms to rake the dried seaweed and bury it to strengthen dunes. Natural “beach litter” such as algae and grasses can enhance the growth of dune vegetation when placed near native dune plants.

A beachgoer stands near seaweed that washed ashore on March 16, 2023 in Fort Lauderdale, Florida. Reports indicate that this summer, a huge mass of sargassum seaweed that has formed in the Atlantic Ocean is possibly headed for the Florida coastlines and shores throughout the Gulf of Mexico. The sargassum, a naturally occurring type of macroalgae, spans more than 5,000 miles. (Joe Raedle/Getty Images)
A seagull walks over seaweed.
A seagull walks over seaweed that washed ashore on Thursday in Fort Lauderdale. (Joe Raedle/Getty Images)
Two beachgoers walk past seaweed on a beach.
Seaweed on a Fort Lauderdale beach on Thursday. (Joe Raedle/Getty Images)
A tractor plows seaweed on a beach.
A tractor plows seaweed on a beach in Fort Lauderdale on Thursday. (Joe Raedle/Getty Images)
A footprint near seaweed on a beach.
A footprint near seaweed on a beach in Fort Lauderdale, Thursday. (Joe Raedle/Getty Images)
Beachgoers walk past seaweed that washed ashore.
Beachgoers walk past seaweed that washed ashore on Thursday in Fort Lauderdale. (Joe Raedle/Getty Images)
A brown leashed poodle sits on seaweed in the sand.
Jason the dog lay on seaweed that washed ashore on Thursday in Fort Lauderdale. (Joe Raedle/Getty Images)