(NEXSTAR) – Massive clumps of smelly, toxic seaweed threaten to wash up on beaches across Florida and the Caribbean again this year.

Last month, the bloom "increased so substantially that the abundance reached a new record from all previous December months," researchers at the University of South Florida Optical Oceanography Lab said.

This type of seaweed, called sargassum, exploded in abundance last month. One million metric tons of sargassum in the central Atlantic in November rapidly grew to 5 million tons by December. That's more than has ever been observed in the month of December.

"This indicates that 2024 will be another major Sargassum year," the researchers wrote.

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Sargassum blooms in the Caribbean Sea and Gulf of Mexico in Dec. 2023 (Credit: USF/NOAA)

The problem with sargassum isn't really when it's floating out in the ocean. In moderation, it can actually create a healthy habitat for sea creatures.

But as it washes ashore and rots, the algae smell like rotten eggs. It can cause breathing issues for people with sensitivities and asthma.

The size of these blooms, and the destruction they cause, has really ramped up over the past decade. "Before 2011, we never saw anything like this," Brian Barnes, a research professor at the University of South Florida who studies sargassum, told Nexstar's WFLA last year.

The good news is that basically no sargassum was found in the Gulf of Mexico, and only a relatively small amount (120,000 tons) was found in the Caribbean Sea. But that's expected to change over the coming months. Scientists anticipate the band of seaweed will keep growing more abundant, and currents will bring pieces of it westward.

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Last year, the sargassum mass grew to 13 million tons. Not all of that washed up on beaches, of course, but the clumps that did come ashore wreaked havoc on parts of Florida's coast, and posed major challenges for the tourism industry over spring break and summer.

If beachgoers do observe sargassum washing up on shore, the Florida Department of Health has recommended they avoid touching or swimming near the seaweed. The small creatures that live inside it, like jellyfish larvae, could sting or cause your skin to itch.

The department also suggested using gloves if you have to handle sargassum and closing windows if you live near the beach to avoid breathing issues and bad smells.