SACHA PFEIFFER, HOST:

Good morning. I'm Sacha Pfeiffer.

Within a few days, some big, nasty-smelling blobs of seaweed could reach the Florida Keys. They're part of a 5,000-mile-wide bloom of algae known as sargassum. Blooms are common, but scientists say they're getting bigger. And this one might be the largest in history. It could blanket some beaches from Florida's Atlantic coast through the Caribbean and up into the Gulf of Mexico. It's so big it can be seen from space.

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