(NEXSTAR) – The Great Atlantic Sargassum Belt is thriving, “setting a record abundance” for this time of year, according to a new report released Friday.

All that abundance – an estimated 13 million tons, University of South Florida (USF) researchers say – is bad news for beaches in the Florida Keys and the Caribbean this summer. As it washes ashore and rots, the algae smell like rotten eggs. It can cause breathing issues for people with sensitivities and asthma.

Satellite images show the 5,000-mile-long belt of seaweed growing denser, and the bloom hasn’t even reached its peak yet. The USF researchers anticipate the seaweed masses will reach their largest size in June or July.

The seaweed belt stretches from the west coast of Africa to the Gulf of Mexico, but researchers say the bloom isn’t one continuous blanket of seaweed. The clumps and mats of loosely connected sargassum cover less than 0.1% of the ocean’s surface, the report said.

Still, even a portion of that 13 million tons of seaweed is enough to wreak havoc on beaches during the peak summer tourism season.

“Major beaching events are inevitable around the Caribbean, along the ocean side of Florida Keys and east coast of Florida, although the exact timings and locations are difficult to predict,” wrote the USF researchers.

In Florida, the biggest impact will be to the southeast coast, from Miami to Palm Beach, and the ocean side of the Florida Keys, Hu said. Florida’s western side will be mostly spared, explained Chuanmin Hu, who tracks the belt as a researcher at USF’s College of Marine Science.

“Only the portion between Panama City and Mobile Bay may receive some variable amount of seaweed, and this will be later in the year (perhaps May) if it does happen,” Hu told Nexstar.

Satellite images taken in March show the bulk of the mass is still out in the Atlantic Ocean, but traces can be seen coming up into the Caribbean Sea and the Gulf of Mexico.

Some sargassum has already started washing up in Florida, the health department said, but the worst is still to come.

“As previously predicted, although the peak month of June or July is several months away, there is already a sign that this year’s Sargassum bloom will likely be the largest ever recorded, with major impacts throughout the next few months,” the report reads.