Tons of stinky, brown sargassum headed to Florida beaches. Where it's going, what we know

Yahoo

16-05-2025

It's heating up, Memorial Day weekend is coming, and everyone's heading to the beach.
Unfortunately, so are tons of toxic seaweed.
Sargassum is a beneficial resource in the Atlantic. But on Florida's beaches, sargassum piles up, produces an epic and harmful stench as it rots, and hosts organisms that can irritate the skin. Not the beautiful sun, sand, and surf experience beachgoers are hoping for, which can be a problem for coastal areas in the Sunshine State dependent on tourism.
The annual sargassum bloom, a vast floating brown blanket of seaweed stretching across 5,500 miles in the water between Africa and the Caribbean, is encroaching on Florida's coasts and spreading into South Florida waterways. And there's a lot more than usual this year.
In April, the University of South Florida estimated this year's bloom is already at 31 million metric tons, '40% more' than the previous record from June 2022, Brian LaPointe, a research professor at Florida Atlantic University's Harbor Branch Oceanographic Institute, told CNN.
The sargassum level in March broke records with an estimated 13 million metric tons, topping the previous March record of 12 million metric tons, according to officials with the University of South Florida who track the blooms. The peak months for sargassum invasion are June and July, but blobs of the naturally occurring type of macroalgae have been spotted along our shorelines since March.
According to the Florida Fish and Wildlife Conservation Commission, sargassum contains pelagic species of brown seaweed that originate offshore in the Atlantic Ocean and float on the ocean surface.
"Sargassum provides many marine ecosystem benefits, including providing habitat for an array of animals such as crabs, shrimp, sea turtles, and fish," FWC writes. "It also serves as a primary nursery area for a variety of economically important fishes such as mahi mahi, jacks and amberjacks."
Sargassum season hits its peak from April to August, during the warm months. Since 2011, it has been more abundant in the Central Atlantic Ocean, the Caribbean Sea, and the Gulf of America (formerly Mexico) as rising ocean temperatures provide a welcoming environment.
"The Florida Fish and Wildlife Conservation Commission (FWC) and the Florida Department of Environmental Protection (DEP) are currently monitoring a large Sargassum bloom and are communicating regularly via routine coordination calls to plan and share current status updates, forecasts, impacts, and trends related to Sargassum in Florida waters," rthe FWC said.
The CariCOOS sargassum map shows the bulk of the massive bloom currently surrounds the Lesser Antilles east of the British Virgin Islands and Puerto Rico.
However, sargassum has already been spotted along the Florida coast from St. Augustine down to the Keys.
An experimental tracking map from the National Oceanic and Atmospheric Administration shows where sargassum is likely to wash ashore. As of May 6-12, most of the coast of Florida was under low risks of sargassum and there was a medium risk by the Big Bend coast in North Florida.
NOAA also shows medium risks in some areas of Cuba and Mexico, and high risks in parts of Mexico, Jamaica, Punta Cana, San Juan and Central America.
To check the water quality and algae blooms near you, click here to see USA Today's database.
Why do we measure sargassum? Sargassum blob at record-challenging amount
'Sargassum has been around for eons. Colombus ran into it right in the Sargasso Sea,' La Pointe told CNN. 'But what we are seeing now is above and beyond what we had historically.'
Experts say there are several conditions contributing to the record bloom in 2025:
Rising ocean temperatures provide a more welcoming environment
Concentrations of nitrogen and phosphorus are pouring into the Atlantic from the Amazon River, which is coming out of two years of extreme drought, and feeding the bloom
There may also be more nitrogen in the water from burning fossil fuels or dust from the Sahara Desert in the atmosphere
Sargassum has historically been largely restricted to the Sargassos Sea, a region of the western North Atlantic Ocean surrounded by four currents. Massive sargassum blooms on our coast are fairly recent, starting in 2011. What happened?
A modeling study published this year in Nature Communications Earth & Environment suggests why: the 2009–2010 North Atlantic Oscillation (NAO), a rare and extreme climatic anomaly.
According to the study, powerful westerly winds and a change in ocean currents may have moved sargassum into tropical waters farther south, where nutrient-rich waters and warm temperatures led to explosive growth.
In the water, sargassum is considered harmless to people, although the seaweed can also host tiny sea creatures that can cause skin rashes and blisters, according to the Florida Department of Health.
On land, sargassum rots and produces hydrogen sulfide and ammonia, which smells similar to rotten eggs. It can irritate the eyes, ears, and nose. People with asthma or other breathing illnesses may have trouble breathing if they inhale too much of it.
That doesn't mean you have to avoid the beach. Moving air in open areas like beaches usually dilutes the gas to non-harmful levels.
If you don't have any open wounds, you should be OK to swim in waters with sargassum. However, it is still recommended by FDOH to avoid touching or swimming near it.
The FWC asks those who wish to report sargassum blooms to go to the NOAA and USF's experimental Sargassum Inundation Report.
Contributing: Kimberly Miller, Palm Beach Post
This article originally appeared on Treasure Coast Newspapers: Sargassum in Florida for 2025? Seaweed reaching record levels