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