Sargassum in St. Barts: where to swim today, beach by beach

Live answer: today's status in St. Barts is shown beach by beach on the map and list above, re-assessed every morning from the official bulletins. Green dots (score 0-1) mark the clear beaches, yellow or orange (2-3) a moderate but swimmable amount, red or black (4-5) the landings to avoid. On most days several beaches are green even when others are loaded. Be aware: conditions can flip within 24 to 48 hours depending on wind and currents — a clean beach this morning can get a landing tomorrow. So the reliable habit isn't to memorise "this beach is good", but to re-check the day's score right before you head out.

Sargassum is a floating brown seaweed (genus Sargassum) that drifts in huge rafts across the sea. The phenomenon has surged since 2011: pushed by tropical Atlantic currents, it crosses the ocean from a vast belt between Africa and Brazil before washing ashore in the Caribbean, in St. Barts as elsewhere. Out at sea it is useful — it shelters fish, turtles and crabs. The problem is the massive landings: piling up on the shore, the seaweed rots within two or three days and releases foul-smelling gases. It's a natural process, but on an unprecedented recent scale, now closely tracked by scientific agencies and local authorities.

Landings mainly hit the north- and east-facing (windward) beaches: St-Jean, Lorient, Anse des Cayes, Grand Cul-de-Sac, Petit Cul-de-Sac and Anse Maréchal.

But "affected" doesn’t mean "off-limits": outside a heavy landing, these beaches are often still swimmable. The leeward south/west beaches are simply the calmest more often. The day’s per-beach score is the only real judge.

Often on the south and west (leeward) side: Gouverneur, Grande Saline, Flamands, Colombier and Shell Beach in Gustavia are generally spared, sheltered from the north-easterly Atlantic swells.

That said, you don’t have to chase "zero sargassum": a beach with light or moderate seaweed is perfectly swimmable. Confirm on the map on the day.

The season mainly runs from March to October, often peaking between April and August — but it varies a lot from year to year in St. Barts. Some years are nearly spared, others break records. A landing lasts from a few days to several weeks, and there's no guaranteed end date: it all depends on the rafts drifting in from the tropical Atlantic, the currents and the wind direction. In practice, there are calm windows even at peak season, and a landing is still possible off-season. That's why a daily, beach-by-beach update is far more reliable than a seasonal average for deciding where to swim.

In the vast majority of cases, no: a beach with light or moderate sargassum poses no risk for a swim in St. Barts. The risk appears during heavy, prolonged landings: as it decomposes, the seaweed releases hydrogen sulfide (H₂S) and ammonia, a rotten-egg smell. At high concentration these gases can bother sensitive people — asthmatics, infants, pregnant women — and tarnish jewellery and electronics. Authorities evacuate the most exposed spots (black score). For visitors the rule is simple: as long as the smell stays faint and the score is below red, the beach is fine. That's exactly what the smell index shown for each beach captures.

Partly, yes. Forecasting rests first on satellite monitoring of the offshore rafts: imagery spots the mats tens of kilometres from shore, giving a window of a few days depending on currents and trade winds in St. Barts. Longer term, monthly bulletins (NOAA, University of South Florida) estimate how much seaweed is in the Atlantic, and thus the risk for the coming weeks. FanGass combines these satellite forecasts with the official weather bulletins to anticipate, beach by beach, where a landing is likely. As no forecast is 100 % reliable — the wind can change everything overnight — it's the daily update that makes the difference.

Each monitored beach in St. Barts gets a 0-to-5 score and a color. Green (0-1): clear, go for it. Yellow (2): some seaweed, perfectly swimmable. Orange (3): a moderate, visible amount, but still swimmable — plenty of people go in, your call depending on the day's smell. Red (4): heavy landing, it stinks, skip it. Black (5): evacuated zone. The rule to remember: only red and black are really to avoid; below that, a swim is fine. A smell index (none / light / strong) completes the score, because it's often the rotting smell, more than the seaweed itself, that ruins the outing.

No need to cancel a holiday in St. Barts: there’s almost always a swimmable beach, and most stay swimmable even with light to moderate sargassum. The south/west beaches (Gouverneur, Saline, Flamands) are often the calmest on heavy days; but there’s no need to write off St-Jean or the whole north side. Best move: check the day’s per-beach score.

Every morning, FanGass aggregates the official monitoring bulletins (Météo-France Antilles, NOAA AOML, the University of South Florida monthly outlook, regional bulletins), cross-checks them against satellite imagery of the offshore rafts, then distills it all into a 0-to-5 score per beach in St. Barts. On-the-ground user reports adjust the scores live when several agree, and everything is re-assessed daily. The service is free, published by the Katchak agency.