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It’s taken over beaches from Florida to the Caribbean, causing one island nation to declare a state of emergency.

By Marisa Spyker

If you live in South Florida, you may have noticed your regular feet-in-the-sand beach walks feeling more like obstacle courses for avoiding masses of seaweed.

Since 2011, scientists have been observing an unexplained influx of brown blooms floating in the Caribbean and Atlantic and inevitably finding their way to the tropical shorelines of some of our favorite vacation spots. This year has been particularly slimy, with record-high blooms observed via satellite imagery—and predictions that the seaweed may continue beaching through August. But what is this stuff, other than a nuisance on beach days?

Known as Sargassum seaweed, the thick—and pungent—plant hails from the Sargasso Sea (a patch of the North Atlantic). Some research suggests that the masses of seaweed drift down from the Sargasso Sea, while others suggest the seaweed pileup is the result of accumulation in the equatorial Atlantic. No one knows the reason for the sudden influx, though some point to changing wind patterns and climate change.

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Regardless of why, the seaweed brings both benefits and drawbacks to beaches. For marine life, huge mats of seaweed block essential UV rays from corals and other organisms that need it. It can also trap small animals like crabs and sea turtles. On the other hand, some fish and sealife can use the seaweed for food and shelter. On land, it can protect beaches from wind and wave erosion.

Sargassum seaweed poses no harm to humans, other than a slight irritation of the olfactory senses. Some tourism-dependent islands in the Caribbean, however, are feeling the brunt of the blow, with problematic seaweed pileups prompting Barbados to declare a state of emergency, and a hotel in Antigua to close its doors through September. In response, governments are thinking fast for ways to either remove the seaweed or mix it with beach sand.

Have you encountered this strain of pesky seaweed on your local beach?