Updated November 2026 · By Terry Barkhuizen, NOM-08 certified tour guide (credential N012608). Sargassum changes daily with wind and currents; always check a current map before choosing a beach.
Part of our Plan Your Trip guide.
Sargassum is a floating brown seaweed that drifts across the Atlantic and, in recent years, has washed onto Caribbean beaches in large quantities – including Cancun, Playa del Carmen, Tulum and Cozumel’s east coast. It’s now one of the most important things to understand when you plan a summer beach holiday here. The good news: it varies enormously by day and by beach, it never affects cenotes, ruins or lagoons, and there are good ways to plan around it.
Quick answer
- Season: usually from around April or May to September or October, with the heaviest arrivals in summer and minimal amounts from November to the end of the year.
- 2026 was a record year: by early September the Mexican Navy had collected more than 123,000 tonnes in Quintana Roo, compared with about 93,000 tonnes in all of 2025.
- Check before you go: the Quintana Roo sargassum monitoring network publishes a colour-coded “traffic light” map of beaches.
- Plan B: cenotes, Maya sites, Bacalar, and the sheltered west coast of Cozumel.
What sargassum is (and isn’t)
Sargassum is a natural, free-floating algae that grows in the open Atlantic. Changes in ocean conditions have produced huge blooms in recent years, carried by currents and winds into the Caribbean. At sea it’s a habitat for marine life. On the beach, large piles turn brown, smell as they decompose, and can make swimming unpleasant. Fresh seaweed in the water is generally harmless to touch, but decomposing piles release gases – avoid lingering beside large rotting accumulations.
How to check conditions
- Quintana Roo sargassum monitoring network: publishes a beach-by-beach “semáforo” (traffic light) map on social media, from blue (no sargassum) and green (low) through yellow and orange to red (excessive).
- Satellite viewers such as UNAM’s sargassum monitoring project show seaweed rafts offshore.
- Hotels and local webcams – ask your hotel how its beach looks that morning.
Conditions change within hours as wind and currents shift, so check on the day.
Where it’s usually lighter
- Isla Mujeres’ Playa Norte – sheltered north-west-facing beach. See the Isla Mujeres guide.
- Cozumel’s west coast – protected from the open-sea currents that bring seaweed to the east side.
- Cancun’s north-facing beaches – often cleaner than the east-facing Hotel Zone beaches, though not immune.
- Bacalar – a freshwater lagoon inland, unaffected.
Beaches between Puerto Morelos and Tulum, and Cozumel’s east coast, are often among the more affected in heavy seasons.
Plan B on seaweed days
- Swim in a cenote – see cenotes near Tulum and near Playa del Carmen.
- Visit Coba, Tulum ruins or Chichen Itza early in the morning.
- Float the Maya canals in Sian Ka’an.
- Take the ferry to Cozumel’s west-coast reefs – see the Cozumel ferry guide.
- In summer, whale shark trips head offshore, away from coastal seaweed.
Booking a summer trip
- Choose a base with good inland day trips (Playa del Carmen or Tulum) rather than a resort where you’ll only use the beach.
- Prefer flexible bookings, and look for hotels that clean their beaches daily or have good pools.
- If a pristine beach is the only goal, December to April is the safer window. See the best time to visit.
Frequently asked questions
Is sargassum dangerous?
Fresh sargassum in the water isn’t dangerous for most people. Large decomposing piles on the beach give off unpleasant gases, so avoid sitting next to them for long.
Does sargassum affect cenotes?
No. Cenotes are inland freshwater pools and are never affected.
When is there no sargassum?
Arrivals are usually minimal from around November to early spring, though occasional winter arrivals happen.