Riviera Maya beaches from the air

There is some sargassum, although in moderate amounts overall. In the first photo, a thin line has washed up along the sand and a few patches float close to shore. The water further out is clear and blue.

In the second photo, the main town beaches have a thicker line at the water's edge but the water along the shoreline looks clear.

Punta Esmeralda continues to show the heaviest sargassum in Playa del Carmen, consistent with the ground photographs of recent weeks. A thick layer covers the waterline and has been heaped along the sand beside the palapas, and the water across the bay is brown well beyond the breaking waves. Behind the beach, the cenote lagoon and the channel that joins it to the sea are dark, in clear contrast with the white sand around them.

On October 2 most beaches between Playa Cisne and Punta Esmeralda had at least some sargassum. At Playa Cisne, long bands of sargassum floated offshore among the moored boats and against the containment barriers, and a line had settled along the shore.

At Calle 72 and Playa 88 a continuous line of sargassum ran along the waterline. At Playa 88 the barriers were holding a large mass of sargassum offshore, while the water close to the shore was tinted brown.

Punta Esmeralda was the worst affected beach on this stretch. A thick layer of sargassum covered the shoreline and turned the water brown across the bay, while the cenote lagoon behind the beach remained clear and green.

On September 25 most of the centre of Playa del Carmen remained clear. The water across this stretch kept its blue and turquoise colour, although some brown-tinted water reached the shoreline near Calles 38 to 44. Playa Mamitas has been the most consistent beach in Playa del Carmen for some time.

Conditions deteriorate north of Calle 44. From Playa Cisne through Calle 72 and Playa 88, and on the approach to Punta Esmeralda, sargassum has settled along the shoreline and the water close to the shore is tinted brown.

Punta Esmeralda showed the poorest conditions on this coast. The water along the beach has lost its blue colour entirely, and the discoloured water appears to be entering the channel that connects the sea to the natural cenote.

Around September 13 and 14 the Riviera Maya received a fresh round of sargassum. Most of the centre of Playa del Carmen recovered very quickly, and by the 18th this stretch was reading clear across most of its length.

What the frame shows is the colour people actually come to the Caribbean for: deep blue offshore, turquoise over the sand, and the dark patches inshore reading as reef and seagrass rather than floating material. The containment line is visible running down the left of the frame.

Calle 44 reads the same way. The sand is open and white, the water inside the barrier is clear, and the darker shapes under the boats are reef rather than sargassum.

This is the part of the pattern worth holding on to. Sargassum volumes have risen every year, and seasonality still matters, but not in the way it is usually described. It is not that occasional sargassum stops arriving outside the peak months of June, July and August. It is that outside that window the coast recovers quickly when a mat does reach the shoreline, and the total volume is less.

The long brown band running down the left of this photograph is sargassum held offshore by the containment line. Behind it, much less sargassum is reaching the shore, and parts of the enclosed stretch are free of floating material. On this section, on this day, the barrier is doing its job.

Some of it always gets through. Inshore of the line the water has turned brown in patches and the turquoise has gone. That is the honest limit of a containment barrier: it intercepts the bulk of the incoming sargassum, it does not close the coast off. Conditions can also differ sharply along a single barrier, with clear water at one end and discoloured water at the other at the same moment.

Punta Esmeralda is the clearest case on this coast. The cove beside the cenote outlet is a flat dark brown, closer to coffee than to seawater, while the water a short distance out is still green. This beach is famous for exactly that colour, a freshwater spring running straight into the Caribbean, which makes the contrast hard to ignore.

Access to Punta Esmeralda is currently closed, and the closure is not entirely a sargassum measure. The municipality shut the entrance on August 31 for around three months of rehabilitation work, roughly 23 million pesos on the access road, pedestrian access and the facilities, and has pointed visitors to Playa 88 in the meantime. Sargassum is part of the reasoning, since the road is being rebuilt to carry the heavy machinery used for collection, but the closure is a construction project rather than a response to beach conditions.

Discolouration of this kind is what researchers call a sargassum brown tide. As the mats decompose they release a leachate that stains clear water a brown, tea-like colour. The term was coined by researchers working in the Mexican Caribbean, who recorded what the discoloured water does to the shallows: less light reaching the seabed, oxygen falling to hypoxia or anoxia, lower pH, and heavy nutrient loading. During the 2018 influx, researchers recorded 78 species killed in the Puerto Morelos reef lagoon, in water discoloured the same way.

The useful lesson for anyone choosing a beach sits in the contrast between these two frames. A brown tide can fill the water while the sand above it looks reasonably clean, either because crews have cleared the beach and the leachate remains, or because the mass is rotting offshore where the barrier holds it. A cleared beach does not guarantee clear, swimmable water.

Conditions near the cubes were close to perfect this morning. The water is transparent turquoise and the shoreline is clean.

Further south, along Forum, Chac Mool and Delfines, some sargassum has accumulated along the shoreline. The beach remains easily swimmable, and the water beyond the waterline is still clear.

This is consistent with the northern beaches of Cancún generally being cleaner, and with conditions deteriorating as the coast turns south and faces the open sea directly.

Playa 72 was overwhelmed. Cleaning crews were at work during the flight, and the footage gives a fair sense of why the task is so demanding: the volume arriving along this stretch is far beyond what can be cleared in a morning, and the effort required is considerable.

The second flight, over Playa 88 and Playa 72, shows the containment barriers intercepting part of the material but by no means all of it, and the water inshore of the line remains brown. That is consistent with our broader assessment of how effective the barriers are: they reduce what arrives, they do not prevent it.

At Punta Esmeralda the water was among the worst we have seen anywhere in the Riviera Maya: a dark, coffee-like brown rather than any shade of blue, despite noticeably less sargassum settled on the sand.

That contrast is the reason a beach cannot be judged on its shoreline alone. A stretch can look reasonably clean underfoot while the water in front of it is unswimmable in appearance, and the reverse also occurs. Both readings belong in an assessment, which is why our scores account for the sand and the water together.

This flight is held over the lighthouse at Punta Cancún, the promontory that divides the northern shore of the hotel zone from the eastern one. Playa Caracol lies immediately to one side and Playa Gaviota Azul to the other, which makes the point a useful vantage: the water around it is transparent, turquoise and free of sargassum.

The northern beaches of Cancún sit in the lee of the point and of Isla Mujeres beyond it, and they commonly present better conditions than the exposed eastern shore. This footage is consistent with that pattern.

This first flight runs the shoreline across Playa 88, Playa 72 and Playa Pelícanos, three adjoining beaches, and the variation within that single stretch is considerable. Some sections carry brown, discoloured water close in, while others a short distance away are visibly clearer. This shows the importance of segmenting beaches and of publishing precise data for each rather than one reading for the whole coast.

The more encouraging part of the picture is on land. The beaches are not overwhelmed at the waterline, and there is very little visible deposit on the sand, which means little or no rotting sargassum ashore.

The second flight heads deeper over the ocean. The containment barriers are visible from above, with a sargassum vessel working the line, and further from shore the Caribbean recovers its turquoise colour. It is a useful reminder that the discoloured band can sometimes be a coastal phenomenon rather than a condition of the whole sea.

Seeing the barriers and the vessel in the same frame also gives a sense of scale that no photograph from the sand provides: the length of the line, and how much of it is being worked at any one time.