Belize Pulse

Why the seaweed keeps coming

12 September 2026 · Belize Pulse · 10 min read

Every resident of Ambergris Caye has a sargassum story: the morning the beach in front of the house was brown to the horizon, the week the smell got into the electronics, the Easter everyone drove to Secret Beach because it was the only clean sand on the island. This post is the long answer to the question behind those stories. Not “is it bad today,” which Belize Pulse now shows at the top of the home screen, but why, and whether it ends.

As with our power post, everything here is drawn from published science, government and Met Service documents, and the local press. Sources are linked. Where the record is unclear we say so.

The short answer

Since 2011 the Atlantic has grown a permanent belt of floating seaweed that did not exist before, stretching at its peak nearly 9,000 km from West Africa to the Gulf of Mexico. It holds tens of millions of tonnes and, according to the latest research, now largely feeds itself. The trade winds and the westward current deliver a slice of it to our reef every year from about February to October. The east-facing beach takes it, the lagoon side doesn’t, and nothing any Caribbean government has tried has done more than manage it locally.

So it is, as one reader put it, intractable in the way the electricity is. The useful things are knowing when it is coming, removing it fast, and being honest about what the money buys.

Where it comes from

Pelagic sargassum is a brown seaweed that lives its whole life afloat, never touching the seabed, reproducing by breaking apart. In ordinary quantities it is a nursery: the Gulf and Caribbean Fisheries Institute counts more than 120 fish species and 120 invertebrates sheltering in it, including baby turtles and tuna. The problem is quantity.

In 2019, scientists led by the University of South Florida published the satellite record in Science: a “great Atlantic Sargassum belt” visible every year since 2011, which in June 2018 stretched 8,850 km and held more than 20 million tonnes (Wang et al., Science, 2019). Their best explanation for the start was nutrients, from Amazon River discharge and West African upwelling. A 2020 study traced the seed population to an unusual winter in 2009–10, when shifted westerly winds blew seaweed from the Sargasso Sea into the tropical Atlantic, where it found the nutrients to stay. A 2021 paper found the seaweed’s tissue holds 35 percent more nitrogen than it did in the 1980s, fingerprinting river-influenced coasts. And a 2026 paper in Nature Communications argues that the belt has crossed a threshold: the community of organisms living in the aging mats now recycles enough nutrients that the belt sustains itself, regardless of what started it.

Scientists still argue about the weights, including how much Saharan dust and warming matter. Officials often say “climate change” in one breath; the 2026 work suggests warming actually works against growth by stratifying the ocean, and is being outweighed by the recycling. The honest one-liner is that the belt is a new ocean feature with several causes, none of which are going away.

The numbers tell the trend. USF’s monthly satellite estimates for the whole Atlantic put the record at 37.5 million tonnes in May 2025, and June 2026 at 33.6 million, the second-largest year ever (USF Sargassum Watch bulletins). The pattern year to year is not a rise but a set of records with quiet years in between: 2022 record, 2023 early collapse, 2024 quiet, 2025 record, 2026 nearly so.

Why the east beach, and why not Secret Beach

Ambergris Caye is about 40 km long and 1.6 km wide, and the barrier reef runs roughly 300 metres off the northern east coast. The trade winds blow from the east; the Caribbean current runs west. Mats that reach the reef pile straight onto the windward beach, through the cuts and over the crest. The west side faces the lagoon and gets none. That is why every season’s press has the same two sentences: the downtown beaches and the long undeveloped stretches north and south are buried, and Secret Beach on the northwest shore “has none” (San Pedro Sun, 2025).

Within the east coast the worst-hit places named in 2025 were the town beaches, the far north around Bacalar Chico and Robles Point where marine die-offs were reported between beach and reef, and Mexico Rocks, where snorkel guides said the corals were “not even visible” under the mats.

What it does

To people. Rotting mats release hydrogen sulfide, the rotten-egg gas, from about 48 hours after beaching, plus ammonia. In 2025 the Polyclinic saw eye irritation cases and residents reported headaches, rashes, and sleeplessness; beach workers reported sinus and throat problems “because they have to sit and smell this all day for days at a time,” and the gas corroded TVs, air-conditioner boards, and jewellery (Ambergris Today, 2025). The official Tourism Board guidance is to avoid prolonged contact and swimming beside affected water, to get sargassum out of the water within 48 hours, and to keep asthmatics, infants, the elderly, pregnant women, and dogs away from enclosed rotting mats. One thing worth knowing: your nose stops registering hydrogen sulfide quickly, so smell is not a safety gauge.

To the reef and the fish. Thick mats cut light and oxygen. Belize Barrier Reef Watch confirmed deaths of lobsters, crabs, urchins, and moray eels in 2025, and fishers described juvenile sardines, bonefish, and snapper dying: “the babies are dying.” Studies from the Mexican Caribbean show seagrass losing most of its root mass under repeated “brown tides,” with recovery measured in years or decades.

To business and the beach itself. Bookings on the island were reported down as much as 30 percent in 2025; large resorts ran three-shift crews at $20,000 to $30,000 a week. And burying the seaweed on the beach, the traditional fix, takes up to 40 percent sand with every load, which the Ministry of Blue Economy says has made erosion in the south worse.

What has been tried, and what it cost

The San Pedro Town Council keeps roughly one mile of “town core” beach clean, from the Boca del Rio bridge to the library, with 20 to 30 workers a shift. In August 2025 that cost BZ$40,000 to 50,000 a week and removed 190 tonnes in a single week, which the council’s own beach manager called about 40 percent of what was needed (Ambergris Today, Aug 2025). His verdict after trying “big machinery, suction systems, helicopters” was that small pick-up trucks are the only tool that works on this beach.

Hol Chan Marine Reserve launched two shallow-water harvesting boats in April 2025, about BZ$2 million on a Social Security Board loan. By December the assessment was “the machines work, but they cannot work on their own,” and in May 2026 both were down for maintenance (Amandala). Since 2026 the collected seaweed goes to six inland composting sites instead of the beach, where the 80-percent-water material dries over about 60 days into something like sand for nourishment, with arsenic and cadmium content the open question for any product made from it.

The Minister of Tourism said in May 2026 that “$25 million” had already been spent on San Pedro cleanup, currency unstated (Breaking Belize News, May 2026). The Breaking Belize News headline on it was “Twenty five million dollars later and Belize’s beaches are still drowning.” A National Sargassum Task Force has existed since 2018; Cabinet adopted an emergency response plan in July 2025; relief grants of BZ$250,000 and BZ$300,000 have gone to hotels; the Environment Department received Taiwanese-funded satellite monitoring equipment in November 2025, now operated by the Met Service.

For scale, look north. Mexico collected a record 92,783 tonnes from Quintana Roo beaches in 2025 and passed 105,000 tonnes by August 2026. Its navy announced a US$115 million programme in July 2026: 50 km of barriers, six harvesting vessels, and a target of 4,000 tonnes a day captured offshore by 2027 (Mexico News Daily). Mexico’s own estimate is more than US$1 million a year to keep one kilometre of beach clean. That is the benchmark for what “solving” it costs, and Belize’s coastline is not short.

Is it bad today?

This is the part we can actually help with. Belize’s Met Service issues a weekly sargassum outlook, usually on Monday or Tuesday, with a probability and expected impact for San Pedro Town, Caye Caulker, Hopkins, and Placencia, and a map (Met Service sargassum forecast). As of this writing it reads “High chance, Moderate impact” for San Pedro through 15 September. Belize Pulse now shows that line at the top of the home screen every week, with a link to the map, and it will turn amber when the outlook is bad.

For the day-by-day, the University of South Florida publishes a daily satellite image of the water off Belize; brown flecks east of the reef mean mats within a day or two of shore on the trades. The Town Council posts its green, yellow, and red phases on Facebook; red means the crews are at capacity and only the town core gets cleaned. And the old rule of thumb still holds: mats come on the easterlies, thin out when the winds swing in hurricane season, and are usually gone from November to January. Both 2025 and 2026 started by February, earlier than the traditional April.

At your own beach

What to expect

Every scientific source we found expects the belt to persist; the 2019 paper’s phrase was that it “may become the new norm,” and the 2026 paper’s finding that it feeds itself removes the hope that it depends on one bad river year. USF flags a “major year” whenever the December Atlantic total is high, so the bulletin due in early January 2027 is the first real signal for next season.

Nobody has a solution, and the honest officials say so: “No one has yet that rightful magic recipe,” the Tourism Minister said, “the only way to eliminate it is to collect it at sea.” What the record supports as a realistic path for Belize is forecast-driven early warning (already live), capture at the reef cuts and corrals on the beach, removal within 48 hours, inland drying with heavy-metal testing, a use that pays for collection, and steady funding instead of annual emergency grants.

The one-line version

The seaweed is a permanent feature of the Atlantic now. On this island the fight is won or lost in the first 48 hours after it lands, and the only real defence is knowing it’s coming.

Belize Pulse is independent and non-commercial. The weekly outlook on our home screen is the National Meteorological Service of Belize’s, quoted with attribution. Corrections to [email protected].

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