Sargassum in Florida: where to swim today, beach by beach

Live answer: today’s situation shows up beach by beach on the map and the list above, reassessed every morning from the official bulletins. Green dots (score 0 to 1) mark the calm beaches, yellow or orange (2 to 3) a moderate but swimmable presence, red or black (4 to 5) the landings to skip. On most days several beaches sit in the green even when others are loaded. Keep in mind that things can turn in 24 to 48 hours with a shift of wind or current, and a stretch that was clean at dawn can take a landing the next day. So rather than memorizing “that beach is good”, the reliable habit is to check the day’s score shortly before heading out.

Sargassum is a floating brown seaweed (genus Sargassum) that drifts in wide mats across the surface. The phenomenon took on a new scale once a broad belt settled in the tropical Atlantic between West Africa and Brazil: pushed by the currents, the mats cross the ocean, travel through the Caribbean and reach Florida through the Straits. Out at sea they are useful, sheltering fish, crabs and juvenile sea turtles. The trouble starts with mass landings: piled on the sand, the weed breaks down within two or three days and gives off strong-smelling gases. A natural process, but at a scale that research labs and county services now track closely.

The oceanside faces take the brunt, starting with the Lower Keys and Key West: Smathers Beach, Higgs Beach, Fort Zachary Taylor, Sombrero Beach in Marathon and Sandspur Beach at Bahia Honda look south onto the Straits and register the first arrivals. In the Upper Keys, Anne’s Beach on Lower Matecumbe and Cannon Beach at John Pennekamp face the same drift. Further north, Miami-Dade (South Beach, Mid-Beach, Surfside, Haulover, Sunny Isles, Crandon Park, Cape Florida on Key Biscayne), Broward (Hollywood, Fort Lauderdale, Pompano Beach, Deerfield Beach) and Palm Beach (Delray, Lake Worth, Singer Island, Juno) get their share, generally a little later.

But “affected” does not mean “off-limits”: outside a heavy landing these beaches are swimmable on plenty of days, and county crews rake the busiest fronts. The day’s per-beach score is the only real judge.

Because of the Florida Current, the arm of the Gulf Stream that squeezes through the Straits of Florida between the Keys and Cuba before turning north. Mats leaving the Caribbean enter that channel first, which is why the Lower Keys and Key West often register a rise before the mainland does. The current then carries whatever stays afloat up the southeast coast, past Key Biscayne and Miami Beach, then Broward around Fort Lauderdale, then Palm Beach as far as Jupiter. In practice that gives a rough running order, Keys first and Palm Beach last, useful for reading a trend but never a timetable: the wind decides where a raft actually lands, and an onshore easterly can pile weed on Palm Beach while Miami stays clear.

The dependable fallback in the Keys is to turn your back on the Atlantic: the bay and gulf faces are shielded from the main drift by the island chain itself. Founders Park Beach in Islamorada looks northwest over Florida Bay, and Calusa Beach sits on the gulf side of Bahia Honda, so both often stay calm on days when the oceanside beaches are loaded. Same logic on the mainland, where the sheltered corners of Crandon Park and the bay side of Bill Baggs at Cape Florida usually collect less than the open oceanfront.

That said, chasing “zero sargassum” is not the point: a beach with light or moderate weed is perfectly swimmable. Confirm on the map on the day.

The season runs mainly from May to September, with the heaviest weeks often falling in early summer, and it swings a lot from one year to the next. Some years pass almost unnoticed, others pile up. A landing lasts anywhere from a few days to a few weeks and no end is guaranteed: it depends on the mats drifting up from the tropical Atlantic, on the Florida Current and on the wind direction. In practice there are quiet windows in the middle of the season, and an arrival stays possible outside it. That is why a daily update, beach by beach, tells you far more than a seasonal average.

In the vast majority of cases, no: a beach with light or moderate sargassum carries no risk for a swim in Florida. The risk comes with heavy, lingering landings: as it breaks down the weed releases hydrogen sulfide (H₂S) and ammonia, the rotten-egg smell. At high concentration those gases can bother sensitive people, asthmatics, babies and pregnant women, and they tarnish silver jewelry and electronics. Fresh mats can also carry stinging cells picked up at sea, which is why an itchy rash is more common inside the weed line than out in clear water. Counties post or close the worst stretches (black score). For a visitor the rule is simple: as long as the smell stays faint and the score is below red, the beach is worth going to. That is exactly what the odor index shown on each beach sums up.

Partly, yes. The forecast rests first on satellite monitoring of the offshore mats: imagery picks up the rafts tens of miles out, which buys a window of a few days depending on the Florida Current and the wind. On a longer horizon, monthly outlooks (NOAA, University of South Florida) estimate how much weed is sitting in the Atlantic and the Caribbean, and therefore the risk over the weeks ahead. FanGass combines those satellite readings with the official weather bulletins to anticipate, beach by beach, where a landing is likely. Since no forecast is watertight, one night of onshore wind can rewrite everything, it is the daily update that makes the difference.

Every monitored beach in Florida gets a score from 0 to 5 and a color. Green (0 to 1): clear, go. Yellow (2): a little weed, swimming is fine. Orange (3): a visible, moderate amount, but still swimmable; plenty of people go in, you decide based on the smell that day. Red (4): heavy landing, strong smell, better to move on. Black (5): stretch closed off. The rule to remember: only red and black are genuinely worth avoiding, below that a swim is still on the table. An odor index (none, faint, strong) completes the score, because it is often the smell of decomposition rather than the weed itself that ruins the outing.

On the busy fronts, yes. Municipal and county crews rake the tourist beachfront in Miami Beach, Hollywood, Fort Lauderdale, Pompano Beach, Delray Beach and along most of the Palm Beach seafront, usually early in the morning, so a beach can look rough at dawn and fine by mid-morning. State parks and protected shorelines work differently: at Bahia Honda, Fort Zachary Taylor or John Pennekamp, the weed is often left where it lands, because the wrack line holds the sand in place and shelters turtle nests. Worth knowing before choosing between a raked city beach and a wilder one.

No need to cancel a trip to Florida: there is almost always a swimmable beach, and most stay swimmable even with light to moderate weed. If you are worried, the bay faces in the Keys and the raked city beachfronts of Broward and Palm Beach are the easiest fallbacks; but do not write off Key West or Miami Beach outright, they are fine on plenty of days and the sand gets cleaned. Best move: check the day’s per-beach score.

Every morning FanGass gathers the official monitoring bulletins (NOAA AOML, the University of South Florida Sargassum Watch System outlook, county beach services, state health advisories and the local press), cross-checks them against satellite imagery of the offshore mats, and boils it all down to a score from 0 to 5 for each Florida beach. On-the-ground reports from users adjust the scores live when several agree, and everything is reassessed each day. The service is free, published by the Katchak agency.