A massive belt of floating seaweed is on track to make 2026 one of the worst sargassum years on record, with the brown algae already smothering Caribbean beaches and drifting into the Gulf, according to the latest satellite data from the University of South Florida.

The April bulletin from the Sargassum Watch System, run by the USF College of Marine Science's Optical Oceanography Lab, shows sargassum increased in every region tracked.

Nearly all set a record for the month.

Sargassum is a free-floating seaweed that drifts in mats across the open ocean. In small amounts it shelters fish, crabs and sea turtles.

In the volumes now crossing the Atlantic, it piles onto beaches, rots in the sun and releases hydrogen sulfide gas — the rotten-egg smell that has driven tourists off Caribbean sand for more than a decade.

By mid-April the seaweed, which looks a lot like a watery sweet potato casserole with the brown, crusty topping, had spread across the entire Caribbean Sea, with substantial amounts pushing into the Gulf. Huge amounts washed up along many Caribbean shorelines, what USF researchers call “beaching events” in the bulletins issued at the end of every month like this mention in late April:

“Sargassum amount in most regions will continue to increase in the coming months,” wrote Brian Barnes and his fellow sargassum scientists. “Beaching events around the Caribbean and southeast coast of Florida will continue and likely increase.

“The year of 2026 is set to be another major Sargassum year -- and likely to be a record year by summer.”

Researchers at USF’s Sargassum Watch System, which works with NOAA to use satellites to improve forecasting of the algae blooms and their size, warn that the huge mats are growing larger this month as feared.

MORE:

• Atlantic sargassum mass growing early, setting records, eyeing Florida
• Sound at sea, sargassum buries beaches and threatens tourism
• Massive swath of brown algae angles toward Southwest Florida beaches, but need we worry?
• Water Quality Report: Sargassum? What Sargassum?
• Listen to WGCU’s Tom Bayles discussing 2024’s sargassum onslaught on NPR’s All Things Considered with Mary Louise Kelley

The huge mats of seaweed were first recorded growing bigger in 2011 and have been pushing or surpassing previous years’ totals many summers since, creating environmental, ecological and economic problems in many regions, Barnes said.

The increases in sargassum are likely due to the cascade of effects from global warming, which include increasing air and ocean temperatures, which in turn affect ocean currents and provide more nutrients in the water.

Sargassum can, and does, bury beaches in Southeast Florida and in the Florida Keys.

Major beaching events have hit the Lesser Antilles, and lesser ones have fouled Florida's southeast coast.

The USF lab's scientists say sargassum may also gunk up Louisiana and Texas shores.

Southwest Florida has been spared so far, mainly due to the Loop Current.

Environmental reporting for WGCU is funded in part by VoLo Foundation, a nonprofit with a mission to accelerate change and global impact by supporting science-based climate solutions, enhancing education, and improving health.

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