It’s that time of year: Sargassum seaweed returns to our beaches

Last updated on May 3rd, 2025 at 11:59 am

Moderate to high levels of sargassum seaweed are washing ashore onto beaches in South Florida and the Florida Keys, and all signs are pointing to another record year.

According to Coastwatch, a joint research project of the University of South Florida and NOAA, researchers say another record year of sargassum inundation is in the offing.

sargassum seaweed sea ranch lakes broward county
While there were signs of a recent beach cleanup, the seaweed was abundant in Sea Ranch Lakes on Saturday morning, May 3, 2025. Sea Ranch Lakes is in Broward County between Lauderdale-by-the-Sea and Pompano Beach. (Photo via Sargassum Watch)

In a normal year, the sargassum season in Florida begins in March or April and continues through summer. In most years, the hardest hit area is the Florida Keys.

This year may be worse than normal. Based on data accumulated through April, “the total Sargassum amount in the tropical Atlantic, as well as for all regions combined, reached a new historical record.”

On my beach in South Florida (Deerfield Beach), moderate levels of sargassum have been washing ashore in clumps for months, and I have found Portuguese man o’ war embedded in the seaweed. Man o’ war looks like a harmless jellyfish, but its long, invisible tentacles have a nasty sting. Give them wide berth.

sargassum seaweed sargassum deerfield It's that time of year: Sargassum seaweed returns to our beaches
Sargassum seaweed on Deerfield Beach, March 31, 2025. If you look carefully, you can also see the bluish bubble of a Portuguese man o’ war peaking out from the seaweed. (Photo by Bob Rountree)

Sargassum outlook as of April 21, 2025

sargassum map may 2025 florida
Red indicates high levels of seaweed are expected on these beaches and offshore in the coming days. Orange indicates moderate presence of seaweed on beaches and offshore waters. Light blue indicates low levels of seaweed are forecast to wash ashore. The yellow arrows show the direction of currents that carry the seaweed from the Central Gulf to Southeast Florida beaches. The seaweed enters the Gulf via the Caribbean Sea from the Atlantic Ocean. (NOAA CoastWatch)

Sargassum blooms arise in the Central Atlantic annually in December and drift westward into the Caribbean Sea. During spring and summer, ocean currents carry the seaweed north past the Yucatan Peninsula into the Gulf of Mexico, then it’s swept eastward around the Florida Keys and along Florida’s east coast by the Gulf Stream.

sargassum seaweed sargassum deerfield beach 2 It's that time of year: Sargassum seaweed returns to our beaches
Sargassum on Deerfield Beach, 3/31/2025. (Photo/Bob Rountree)

The floating seaweed provides beneficial shelter from the sun and food for fish offshore.

As a fisherman, I am quite familiar with these patches of seaweed, which often form long lines at the edge of the Gulf Stream. Trolling along these lines is often productive for gamefish, especially for schools of mahi-mahi lingering in the shade and nibbling on small fish and crustaceans harboring there.

The seaweed itself is not harmful to human, but decaying sargassum on beaches releases hydrogen sulfide that can impact people with breathing issues.

New research by Florida Atlantic University suggests the pathogen Vibrio sticks to microplastics that merge into sargassum clusters at sea, and while the bacteria has not been detected in sargassum washing ashore, beachgoers are advised to keep their distance from seaweed clusters.

Vibrio vulnificus, one of more than 100 species of Vibrio, sometimes referred to as flesh-eating bacteria, can cause life-threatening food-borne illnesses from seafood consumption as well as disease from open-wound infections, according to the national Centers for Disease Control.

sargassum seaweed Sargassum on the beach It's that time of year: Sargassum seaweed returns to our beaches
Closeup of sargassum seaweed on a beach. (Source: Wikipedia)

You might think seaweed could be removed from the water before it hits our beaches, but that’s against the law because of its value as a shelter and food source for marine life.

Once the sargassum blob hits the beach, it is legal to remove it. Popular tourist beaches rake the seaweed each morning and remove it from beaches, but with the state’s 1,350 miles of shoreline, that’s not possible on every beach.

Resource for you: Sargassum Information Hub


RELATED STORIES


Beach Cams around Florida

Sargassum seaweed arrives in waves, depending on wind direction and currents.

These links will take you to live beach cameras at popular Florida beaches so you can see for yourself in real time.

Surfing area at Deerfield Beach, north of the pier. (Webcam hosted by City of Deerfield Beach)

Atlantic Beaches (North to South)

Gulf Beaches (Panhandle to South)


Sargassum FAQ


What is Sargassum?

Sargassum is a type of floating brown algae, commonly called “seaweed.” These algae float at the sea surface, never attach to the sea floor, and they can aggregate to form large mats in the open ocean.

Where does it come from?

Historically, the majority of Sargassum aggregated in the Sargasso Sea in the western North Atlantic, with some small amounts found within the Gulf of Mexico and Caribbean Sea.

In 2011, the geographic range expanded, and massive amounts of Sargassum moved west into the Caribbean Sea, Gulf of Mexico, and south tropical Atlantic, washing ashore in Florida, Puerto Rico, the US Virgin Islands, and most islands and coastal areas in the Caribbean Sea.

What are the benefits of Sargassum?

Sargassum, in normal amounts, provides habitat, food, protection, and breeding grounds for hundreds of diverse marine species, including commercially important species, such as tuna and swordfish, which feed on the smaller marine life present in Sargassum mats.

If Sargassum reaches the coast in small/normal quantities, it may help to avoid beach erosion.

What are some of the drawbacks of Sargassum?

As Sargassum accumulates close to the coastlines, it can smother valuable corals, seagrass beds, and beaches. As it washes ashore the seaweed begins to decay, attracting flies and other insects.

During its breakdown, Sargassum produces hydrogen sulfide gas, which smells of rotten eggs, repelling beachgoers. 

Sargassum can also impact navigation, block water intake in desalination plants, and impact benthic ecosystems after/if they sink to the bottom of the ocean.

What threats, if any, does Sargassum pose to human health?

Studies of the impact of Sargassum on human health started very recently and this is a topic that needs more time to be fully understood. However, when decomposed, Sargassum releases hydrogen sulfide (a gas) that may cause respiratory health problems. Sargassum is also known to often contain heavy metals that can be toxic to humans and animals.

What about reports of ‘flesh-eating bacteria’ in sargassum?

In the open ocean, researchers at Florida Atlantic University discovered the pathogen Vibrio sticking to microplastics that merge into sargassum clusters at sea.

Vibrio vulnificus, one of more than 100 species of Vibrio, sometimes referred to as flesh-eating bacteria, can cause life-threatening foodborne illnesses from seafood consumption as well as disease, even death, from open-wound infections, according to the national Centers for Disease Control.

Kevin Johnson of Florida Tech’s marine sciences department, says the FAU research “has not demonstrated the sargassum coming onshore is especially dangerous with regard to bacterial infection for people.

Many of the bacteria that are associated with those plastics and sargassum are already present in our environment.”

What you should know about flesh-eating bacteria on beaches, CNN, 6/9/2023

“I don’t think at this point, anyone has really considered these microbes and their capability to cause infections,” says FAU biologist Tracy Mincer. “In particular, caution should be exercised regarding the harvest and processing of Sargassum biomass until the risks are explored more thoroughly.”

Sargassum removed from beaches is frequently used in fertilizers.

Does Sargassum cause skin rashes and blisters?

Sargassum does not sting or cause rashes. However, tiny organisms that live in Sargassum
(like larvae of jellyfish, sometimes called sea lice) may irritate skin if they come in contact with it.

Why did the geographic range for Sargassum expand in 2011?

Researchers are still assessing various hypotheses about the cause of this first documented extreme event. 

One hypothesis proposes that during the winter of 2009–10, winds that typically blow east from the Americas to Europe, strengthened and shifted south more dramatically and persistently than any other time.

This shift in winds triggered a long-distance eastward dispersal of Sargassum, from the Sargasso Sea, toward the Iberian Peninsula in Europe and West Africa.  

After exiting the Sargasso Sea, the Sargassum drifted southward in the Canary Current and entered the tropics.

Once in this new and favorable tropical Atlantic habitat, with ample sunlight, warm waters, and nutrient availability, the Sargassum flourished and has continued to grow.

In addition to changing wind patterns, other hypotheses include other factors, including the outflow of major rivers, nutrient (nitrogen and phosphorus) concentration in the oceans, increases in the amount of phosphorus due to Saharan dust, water temperature, and river runoffs.

Having established a new population, the Sargassum now aggregates almost every year, starting in January/February in a massive belt north of the Equator, along the region where the trade winds converge.

During the late winter and early spring months, the Sargassum moves northward with the seasonal winds and currents. By June, this belt may stretch across the entire central tropical Atlantic. Large portions of this algae are then transported into the Caribbean Sea and Gulf of Mexico via the North Equatorial and Caribbean current systems.

Is the amount of Sargassum in the Atlantic/Caribbean increasing?

Since 2011, large accumulations of Sargassum have occurred every year in the Caribbean Sea, Gulf of Mexico, and tropical Atlantic, but the amount can vary from year to year.

The presence of Sargassum occurs over large areas from the tropical Atlantic to the Caribbean Sea and the Gulf of Mexico.

Sargassum does not extend as a blanket (or blob) covering the full surface of the ocean in these regions. Instead, Sargassum floats in patches of various sizes. Some of these patches reach the coastal areas, including beaches, ports, and even intake systems for drinking water.  

The area that these patches cover has been significantly larger in recent years than prior to 2011.

Sources: National Oceanic and Atmospheric Administration (NOAA) Coast Watch; Florida Department of Health Fact Sheet

16 Comments

  1. Natalia Picardi

    Hi! I am planning to to do Lauderdale by the beach this weekend? How is the. Sargassum? Thank you so much’

  2. Hi. Planning a family trip to Naples Beach July 13-19. Was hearing we may be affected by sargassum weed? Will hate to be there and not be able to swim. Coming from Canada. Also concern about omeba. Should I reconsider visiting at this time?

    • The seaweed glut is easing along the Southwest Florida coast, according to the University of South Florida, and when I looked at the Naples Beach web camera this morning, there doesn’t appear to be any seaweed at all on or near the beach. Here’s a link to a live web cam: https://youtu.be/3VJGu5uD1bM. As for the amoeba, the only amoeba reported by scientists has been attached to microplastics caught up in seaweed far out in the Atlantic Ocean, according to the results of a study by Florida Atlantic University. Even with that study, there is no evidence any human interaction with seaweed has caused any medical issues. Obviously, the decision is yours to make. But personally, I don’t think there’s a lot of reason for concern.

  3. Hi Bob, planning on going to crandon park in key biscayne this weekend. My elderly grandmother is freaking out because she heard about the flesh eating bacteria on the news. Are you familiar with this area? Do you think it’ll be safe to swim? Appreciate you taking your time. Thanks

    • The seaweed seems to be easing up on South Florida beaches for now, so I wouldn’t be concerned. As for the amoeba, there is no evidence that anybody has been affected by “flesh-eating bacteria.” Researchers at Florida Atlantic University have only detected it on microplastics far out at sea, but there is no evidence of them washing ashore with seaweed. Obviously, the choice is yours to make. Personally, I don’t think there’s much of a threat. Here’s a link to a live web cam on Key Biscayne so you can see for yourself. https://keybiscayne.fl.gov/uniquely_kb/kb_beach_cam.php

    • Thank you Bob, you’ve been most helpful. I too think it’ll be fine

  4. We suppose to be going to Key West for a week starting June 17. My mother is concerned too. I’m not sure if we should cancel or not ? Any suggestions would be greatly appreciated.

    • I wouldn’t let a little seaweed get in the way of your trip to Key West. There are far more distractions in Key West than a beach. The five public beaches are scattered around the island, and I doubt they would all have a sargassum problem at the same time. If you are still concerned, call your hotel or the host of your vacation rental. Whatever you do, have fun!

  5. I am planning a weeks vacation in Destin Junee 11th . I just read an article that the brown seaweed can also carry flesh eating omeba. I am now freaking out. Should we consider not going.

    • Kevin Johnson of Florida Tech’s marine sciences department, says the FAU research in the article you read “has not demonstrated the sargassum coming onshore is especially dangerous with regard to bacterial infection for people. Many of the bacteria that are associated with those plastics and sargassum are already present in our environment.”

  6. Hi we are planning a trip to Panama City Beach July 22-29, how bad do you think the seagassum will be affecting the beach?

    • No way to predict, but Panama City Beach is one of those destinations that keeps its beaches clean, especially considering their prime tourist season is summer. I wouldn’t worry about it.

  7. SUSAN HOWARD

    Greetings Bob, I wanted to draw your attention to a news program from today about the Sargassum Seaweed. According to WEAR NEWS, FAU has determined the bacteria vibrio is found in the seaweed. This bacteria is the dominant cause of death in humans from the marine environment. I am planning a trip to John Penningcamp State Park in a couple of weeks and was looking forward to snorkeling. Now I’m not sure it would be a good idea. I have Cancer so I have to be vigilant about such issues. Thoughts? Cheers, Susan

    • Hi Susan: The original FAU press release about this issue seems to focus on beached sargassum, but the level of threat is unknown. It’s likely you’d be snorkeling offshore from a boat at Pennekamp. At sea, sargassum comes in lines and clumps, not highly concentrated like it is on the beach, and it doesn’t start rotting and releasing pathogens until it lands on the beach, or so we’re told. My gut tells me the FAU research is very preliminary. But considering your other issues, I’d talk to your doctors. Good luck beating your cancer.

    • @Bob Rountree, Thanks for the thoughtful reply! I’m still on the fence.

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