Miami's Seaweed Problem
Starts an Ocean Away

If you have spent time on a South Florida beach this summer, you have probably seen it: thick mats of brown seaweed along the tide line, heavier on some days than others, and a run of headlines describing the season in stark terms. The seaweed is sargassum, and 2026 has been a heavy year. Researchers at the University of South Florida's Optical Oceanography Laboratory track the region by satellite and publish a monthly outlook; in their July 31 bulletin they reported that amounts had begun falling in every region they monitor, and that the season's peak month had passed. That is a regional reading, not a measurement of any beach. USF says so itself: its bulletin should not be used to predict conditions at a specific location or beach. This article is not a verdict on the beaches. It explains what is actually happening, and why one beach can look very different from the next.

Sargassum is a brown seaweed, a macroalga, that floats on the ocean surface instead of rooting to the seabed. Small gas-filled bladders keep it afloat, forming rafts and long ribbons that drift with the current. Out in the open ocean this floating habitat is genuinely valuable, sheltering fish, sea turtles, crabs, and other marine life. The problem is not that sargassum exists. The problem is scale, the sheer volume now reaching populated coastlines. When enormous quantities pile up and break down, the same seaweed that supports life offshore becomes a nuisance onshore.

Here is the part that surprises most people. The sargassum washing up in Miami does not come from Miami, or even from Florida. It begins far away, largely in the tropical Atlantic. Since 2011, scientists have tracked a recurring band of sargassum that stretches, in heavy years, from the west coast of Africa to the Gulf of Mexico. Researchers named it the Great Atlantic Sargassum Belt.

Why it formed is a question scientists are still working to answer. There is no single established cause. The EPA's review of the origin and drivers of the Great Atlantic Sargassum Belt points to several contributing factors under study rather than one culprit: changes in ocean nutrients, the upwelling of deep water off West Africa, discharge from major rivers, dust blown off the Sahara, and shifts in temperature and circulation. Different research groups emphasize different triggers. The science is still developing, and anyone who tells you sargassum has one simple cause is going beyond what the evidence supports.

Once the belt forms, ocean currents do the rest. Sargassum rides the equatorial and Caribbean currents westward, through the Caribbean, and toward Florida and the Gulf. The heaviest arrivals along Florida and in the Caribbean typically fall in the warmer months, roughly May through August, though the exact timing shifts from year to year. That is why sargassum behaves like a season rather than a single event: it builds through late spring, peaks in summer, and eases in the fall.

If the belt explains why sargassum reaches Florida at all, local conditions explain why your beach looks the way it does on any given morning. How much lands on a specific stretch of sand on a given day depends on nearshore currents, wind direction and strength, the tide, and the shape of the beach itself. Those variables change constantly. That is why two beaches a few miles apart can look completely different on the same afternoon, and why the same beach can be clear in the morning and covered by evening. It is also why a single dramatic photo is a poor guide to what you will find when you arrive.

The most common worry is health, and it deserves a direct answer. Fresh sargassum floating in the water is generally not considered harmful. The issue begins once it piles up on the sand and starts to decompose. As it breaks down, it releases hydrogen sulfide, the gas responsible for the rotten-egg smell, along with ammonia. The EPA's guidance on the human-health impacts of sargassum inundation events notes that these decomposition-related gases can begin developing after sargassum has remained beached for roughly 48 hours, and that they can irritate the eyes, nose, and throat. The effect is strongest at close range and matters most for people with respiratory sensitivities and for cleanup crews working directly in it. For a typical beachgoer in open air, where wind disperses the gases, the Florida Department of Health's sargassum guidance states that exposure is generally not expected to harm the health of most people. As a practical matter, it is best not to handle piles of beached seaweed directly.

A reasonable question follows: if the seaweed is a problem on the sand, why not remove all of it, everywhere, at once? Part of the answer is that Florida's beaches are sea-turtle nesting habitat. Beach cleaning during sea-turtle nesting season is regulated and must follow nest-survey, timing, and equipment restrictions, and hand-tool cleanup is treated differently from heavy machinery. There are ecological reasons too: a modest amount of sargassum on the sand returns nutrients to the beach system, and removing every trace is neither always permitted nor always the better outcome. Some seaweed is left in place on purpose.

Locally, Miami-Dade County's sargassum and beach-maintenance information describes its routine public-beach maintenance corridor as running from Government Cut to the Broward County line, a span that includes the public shoreline through Sunny Isles, with beach-maintenance crews operating seven days a week. That is the routine baseline. Separately, more intensive collection and removal is concentrated at the spots where sargassum accumulates most heavily, and the methods, timing, and visible results of that work vary with conditions, access, environmental rules, and how much seaweed is arriving. Routine maintenance is not the same as clearing every beach to bare sand each day, and two nearby stretches can differ at the same moment.

Miami is one of many Atlantic and Caribbean communities managing recurring seasonal arrivals. That regional context helps place a heavy local season in proportion without minimizing it.

All of this leads to something practical. Because conditions are so local and change so quickly, the most reliable approach is to check a current source on the day you plan to go, rather than rely on a headline about the season as a whole. Five free public resources are worth knowing, and each one answers a different question. Only one of them shows you the beach itself.

Two habits do more than any single tool. Check wind and tide for the morning you are actually going, and compare two nearby beaches rather than assuming they match. Neither takes long, and both beat a season headline.

For those who own a condominium in Sunny Isles, or are considering buying one, the sensible way to think about sargassum is as a seasonal but recurring coastal condition whose intensity and local effects vary significantly from year to year, beach to beach, and day to day. That framing is more useful than either alarm or dismissal, because it points to specific, answerable questions. Whether you own or are buying, the practical questions are the same: how your building communicates about beach conditions, how amenity access is handled during heavy weeks, and how cleanup near the building is coordinated. Public-shoreline operations are handled by Miami-Dade County within its service area. Private-property responsibilities, building-level operations, and any association-level cost should be verified with the relevant association. GF Real Estate's role is to help you understand a seasonal coastal condition clearly, not to predict beach conditions or their effect on a property.

The system behind Miami's seaweed is large, global in origin, and still being understood. What lands on a given beach, though, is local, seasonal, and now less mysterious: a coastal condition worth understanding on its own terms. If you are weighing what it means for your building or a purchase, we are glad to help you think it through.

Every factual claim above rests on one of the following. They are grouped by what each one is actually good for, because they are not interchangeable.