The accumulation of sargassum in the Atlantic Ocean has reached unprecedented levels in 2025, with an estimated volume of 31 million metric tons, according to data from the Sargassum Watch System (SaWS), an initiative of the College of Marine Science at the University of South Florida (USF). This figure represents a 40% increase compared to the previous record set in June 2022.
- How Many Tons of Sargassum Are in the Atlantic in 2025?
- Which Areas of Florida and the Caribbean Are Affected by Sargassum?
- Why Is There More Sargassum in 2025? Causes and Factors Explained
- What Are the Effects of Sargassum on Health and the Environment?
- What Is Being Done with the Collected Sargassum?
- When Is the Peak of Sargassum Expected in the Caribbean?
The phenomenon, stretching over 5,500 nautical miles from the coasts of West Africa to the Gulf of Mexico, affects key regions in the Caribbean, as well as the coastline of Florida, including the Keys, Key Biscayne, and other tourist areas. Satellite images released by USF and NOAA Coral Reef Watch show the magnitude of the floating algae belt, which threatens to continue growing in the coming months.
The proliferation of this marine macroalgae has environmental, health, and economic consequences, impacting tourism-dependent destinations in Mexico, the United States, and the Caribbean islands. Researchers from the U.S. and Mexico attribute the growth of sargassum to a combination of factors, including climate change, the intensive use of fertilizers, and nutrient discharges from major river basins like the Amazon and the Mississippi.
How Many Tons of Sargassum Are in the Atlantic in 2025?
According to researcher Brian LaPointe from the Harbor Branch Oceanographic Institute at Florida Atlantic University, the increase compared to the June 2022 record was approximately 40%. As he explained in statements to CNN, the growing season has not yet concluded, so the figure is expected to continue rising.
The densest concentrations of sargassum are located in the central and western Atlantic, drifting with currents toward the Caribbean Sea, the Gulf of Mexico, and the east coast of the United States. Monitoring also indicates significant presence off the coasts of Brazil and in the arc of the Lesser Antilles.
Which Areas of Florida and the Caribbean Are Affected by Sargassum?
Recent reports from NOAA Coral Reef Watch and local media like The Miami Herald indicate that sargassum is already impacting the east coast of Florida, with visible accumulations on beaches like Miami Beach and in marinas like Dinner Key Marina. Photographs taken on May 8 document large quantities of algae surrounding boats and piling up on the shore.
In Mexico, the Secretariat of Ecology and Environment (SEMA) of Quintana Roo reported that over 9 kilometers of floating barriers have been deployed off Playa del Carmen, Puerto Morelos, and Mahahual to contain the arrival of sargassum. Governor Mara Lezama stated on social media that these actions are coordinated with the Secretariat of the Navy (SEMAR), which is also conducting offshore collection operations.
Other affected regions include eastern Caribbean islands such as Barbados, Guadeloupe, and Dominica, where local tourism associations have reported a decline in hotel bookings due to the impact of algae on beaches, according to data from the Caribbean Alliance for Sustainable Tourism.
Why Is There More Sargassum in 2025? Causes and Factors Explained
The expansion of sargassum is driven by multiple environmental and anthropogenic factors. Researchers from USF, the Harbor Branch Oceanographic Institute, and the Institute of Engineering at UNAM agree that rising ocean temperatures, the use of agricultural fertilizers, and river discharges are the main drivers of this anomalous bloom.
Dr. Brian LaPointe noted that fertilizers rich in nitrogen, used in intensive agriculture in the United States and Brazil, are carried by the Mississippi and Amazon rivers into the ocean. Under conditions of prolonged drought, such as those recorded in the Amazon basin in 2023 and 2024, the accumulation of organic matter on land is abruptly released when rains return, causing a “first flush” phenomenon with high concentrations of nutrients.
NOAA Coral Reef Watch added that elevated ocean temperatures above historical averages have also contributed to creating favorable conditions for sargassum growth, with thermal anomalies detected since the beginning of the year in the tropical Atlantic and the Caribbean Sea.
What Are the Effects of Sargassum on Health and the Environment?
Sargassum has direct consequences for public health and coastal ecosystems. Upon reaching the shore, the algae begin to decompose, releasing hydrogen sulfide and ammonia. According to studies by the Harbor Branch Oceanographic Institute and the Institute of Marine Sciences and Limnology at UNAM, these gases can cause symptoms such as eye irritation, nausea, and respiratory problems in exposed individuals.
Additionally, the accumulation of sargassum blocks sunlight from reaching the seafloor, affecting sensitive habitats like coral reefs, mangroves, and seagrass beds. The decomposition of the algae also reduces available oxygen in the water, leading to die-offs of species such as fish and crabs.
Heavy machinery used by resorts to remove the algae can also damage the structure of beaches and coastal wildlife, according to environmental reports cited by CNN and the Government of Quintana Roo.
What Is Being Done with the Collected Sargassum?
Facing the magnitude of the problem, researchers and authorities are exploring alternative uses for the accumulated sargassum. Professor Christian Appendini from UNAM noted that applications for the algae are being researched in the production of biofuels, construction materials, water treatment filters, and biodegradable substitutes for plastic.
These investigations are in the experimental phase. One of the challenges is sargassum’s high capacity to absorb heavy metals and contaminants like cadmium and arsenic, raising questions about its safety in industrial or agricultural applications.
On the other hand, some pilot projects have considered the controlled sinking of sargassum in the seafloor as a strategy to capture atmospheric carbon, though this practice requires environmental validation to avoid negative ecological consequences.
When Is the Peak of Sargassum Expected in the Caribbean?
According to historical data from the SaWS system at the University of South Florida, the period of highest sargassum concentration in the region typically occurs between June and August. Satellite monitoring will continue over the coming months, with special attention on the western Caribbean, the Gulf of Mexico, and the Florida peninsula.
The alert system developed by USF allows local governments, tourism operators, and fishermen to anticipate the arrival of the algae and take containment measures. Through monthly bulletins, researchers publish updated maps detailing the location, volume, and direction of movement of the sargassum belt.
Image: Infobae
