Marine Life & Conservation
The Yucatan Cenotes – A paradise under threat from tourism

An interview with Sam Meacham by Jeff Goodman
A few years ago I made a film for the BBC called ‘Secrets of the Maya Underworld’ and was about the Cenotes and forests of the Yucatan Peninsula, Mexico. Previously I had always promised myself not to ever cave dive as I had a fear of being lost or trapped far underground with no escape route. Then a few very good friends told me of the Cenotes and the incredible wildlife that was associated with them. I had to see for myself.
It was then I met Sam Meacham, an American living near Cancun. He had been exploring the caves and passageways of the Yucatan Peninsula for the previous 18 years and now to date has discovered with other divers 252 known caves and cave systems in that region with a total of 1,103.3 km or 685.5 miles of surveyed passageway between them. Two of the five longest caves on the planet Sistema Sac Actun and Sistema Ox Bel Ha are found close to the town of Tulum.
The Yucatán Peninsula was once a shallow coral reef and now over a few million years has become a porous limestone shelf covered with forest and wildlife. There are no visible rivers; all the fresh water rivers are underground. Being porous, caverns and caves formed where the fresh water collects – hence the Cenotes or water sinkholes.
Recently, the Cenotes have become a great dive destination and the eastern Yucatan coastline an ever developing tourist area for sun worshipers and beach goers. The seemingly uncontrolled developments are taking their toll on this unique ecosystem.
I recently got back in touch with Sam to see if things were improving.
Jeff: Can you just tell us exactly what the Cenotes are and what is so special about them?
Sam: Cenotes are karst sinkholes that occur in Mexico’s Yucatan Peninsula. The Cenotes are windows into the freshwater aquifer of the region and the entrances to the very complex flooded solution cave systems along the Caribbean coastline.
Jeff: The underground water systems give life to the forests above where wildlife is obvious to find, but is there life in the caves as well?
Sam: Most people think of the cave environment as a very sterile place. In fact, there are over 40 life forms so far identified that live in the dark recesses of these caves. The majority are crustaceans and they are all considered extremeophiles because of the conditions they live in. The Cenotes themselves are also magnets for life; this includes a number of freshwater tropical fish species, crocodiles, turtles in the water and birds and mammals (including jaguars) at the surface.
Jeff: How long has man know about the Cenotes?
Sam: There is growing evidence that the caves and Cenotes were accessed by humans during the last ice age, which was 8000-10000 years ago.
Jeff: Did the Maya have any idea about the complexity of the underground waterways?
Sam: It is hard to say if the Maya realized that some of the Cenotes were connected by the intricate and complex cave systems. Many of the underground rivers flow out to the sea in very impressive upwellings; perhaps they put two and two together when they observed this. It was not until the 1980’s that cave divers really began to probe the depths of the Cenotes and really revealed just how complex and extensive they were.
Jeff: Are the Cenotes and reliant ecosystems in any threat now due to the commercial tourist developments?
Sam: There is a very real and continuing threat from the development of the tourism industry along the coastline. Karst landscapes like the Yucatan are very susceptible to contaminants that leach through the porous limestone and into the aquifer.
Jeff: What are the main issues?
Sam: The main issues we face are contamination from solid waste (garbage) and sewage. Once contaminants hit the aquifer there is the high potential for them to be transported through cave conduits and out to the Caribbean Sea. High concentrations of contaminants cause algal blooms that cover the Mesoamerican Reef and kills the corals. If we lose the reef, we lose the protection to the beaches. If the beaches erode, where will the tourists go? Effectively, we risk killing the goose that lays the golden egg.
Jeff: Is anyone listening to the conservation needs of the area or is commercialism taking its full toll?
Sam: Well, I think worldwide conservation efforts are always facing an uphill battle and this area is no exception. But I do think there is a great deal more awareness about the existence and importance of the flooded caves. My personal belief is that the outreach and education about the caves is the only way we can engage the public and effect change.
Jeff: As Divers, how can we help preserve this unique ecosystem?
Sam: If you dive in the Cenotes, it is a great opportunity to perfect your skills particularly your buoyancy and trim. Really, any time you go diving you should be perfecting your skills. We, as divers, are privileged visitors to the underwater environment and must make every effort to protect it.
Jeff: If readers want to learn more where can they get further information?
Sam: Here are a few websites:
Marine Life & Conservation
Make Every Dive Count

The Shark Trust Great Shark Snapshot is back for its 4th year! And this time the Shark Trust are asking you to Make Every Dive Count!
The last week of July will see the return of the Shark Trust’s citizen science initiative: The Great Shark Snapshot. It encourages divers and snorkellers, all around the world, to record the sharks and rays that they see. This year it takes place between the 19th and 27th July. Get ready to dive in!
The event is back for its 4th year, and it is happening in “Shark Month”, more commonly known as July! To coincide with a series of events that celebrate all things shark and ray, including Shark Week and the 50th anniversary of Jaws.
Divers, clubs, centres, charter boats and liveaboards are all encouraged to show their support by organising dives and events throughout the week. As well as gathering vital data, the event will provide a chance to celebrate the incredible shark and ray species that live in our ocean.
Information about the species and numbers of sharks and rays the participants find over the week will be added to the Shark Trust’s Shark Log. This global shark census will, over time, allow shark scientists to build a picture of species distribution and any changes that occur
Caroline Robertson-Brown, Marketing Manager at the Shark Trust said “It is great to see this popular citizen science event back for its 4th year. We are asking divers to Make Every Dive Count this year. To identify. Count and Record every shark, ray and eggcase they see during the week-long event. To organise dives especially to take part. Whether you are diving your local dive site, or on a trip of a lifetime, we want divers to join in on the Great Shark Snapshot in July.”
It is easy to join in. Just go diving between 19th and 27th July and record every shark, ray, skate or eggcase that you and your dive group sees. If possible, take photos and some video footage too. Then make sure that you record your sightings on the Shark Trust Shark Log recordings website or by using the Shark Trust app.
This year we have created a digital guide that puts all the information you need in one handy online guide. Which can be downloaded from the website.
The Great Shark Snapshot is a way for divers to get together, go diving, and do something to help shark conservation. Why not dive in?
Find out more here: www.sharktrust.org/snapshot
Blogs
The Ocean Cleanup Launches 30 Cities Program to Cut Ocean Plastic Pollution from Rivers by One Third by 2030

The Ocean Cleanup, the international non-profit with the mission to rid the world’s oceans of plastic, has announced, at the UN Ocean Conference (UNOC), its plan to rapidly expand its work to intercept and remove ocean-bound plastic pollution.
The 30 Cities Program will scale the organization’s proven Interceptor™ solutions across 30 key cities in Asia and the Americas, aiming to eliminate up to one third of all plastic flowing from the world’s rivers into the ocean before the end of the decade.
This evolution follows five years of learning through pioneering deployments across 20 of the world’s most polluting rivers and represents a key next step in the organization’s mission and the global fight against ocean plastic pollution.
With the 30 Cities Program, The Ocean Cleanup will transition from single river deployments to citywide solutions, tackling the main plastic emitting waterways within each selected city. This follows a key learning from deployments in Kingston, Jamaica, which showed it is possible to scale faster when projects encompass whole cities, as the same set of partners can be involved with all deployments.
To date, The Ocean Cleanup has already prevented 29 million kilograms of trash from reaching the ocean. The organization currently intercepts an estimated 1–3 percent of global river-borne plastic emissions. With the first 20 river deployments close to being fully operational, it is now poised to reduce the plastic pollution flowing into the ocean from rivers by up to a third.
“When we take on an entire city, instead of individual rivers, we can scale faster, reduce costs, and maximize impact,” said Boyan Slat, Founder and CEO of The Ocean Cleanup. “Our analysis shows that strategically deploying Interceptors across just 30 carefully chosen cities can stop up to a third of river plastic pollution worldwide. This is the next big leap toward our ultimate goal of a 90 percent reduction in global ocean plastic pollution.”
City-by-city: a Faster Path to Scaling
Using the latest scientific modeling and on the ground experience, The Ocean Cleanup identified 30 major plastic polluting coastal cities which include:
• Panama City, Panama – First deployment to go live in the coming months.
• Mumbai, India – Mapping of all waterways completed; preparations for first deployments underway.
Furthermore, the organization is developing plans to expand on its existing work to all polluting rivers in:
• Manila, Philippines; Montego Bay, Jamaica; Jakarta, Indonesia; Kuala Lumpur, Malaysia; Bangkok, Thailand and Los Angeles, U.S.A.
Other cities will be announced once the necessary partnerships and agreements are in place. Planning and fundraising activities are underway for all 30 cities. To realize these ambitious plans, the organization is currently also expanding its engineering and operational capacity.
Data Driven Restoration at Scale
Before Interceptors are deployed, each city project begins with an intensive analysis phase. Aerial drones, AI-powered image analysis, and GPS-tagged “dummy” plastics are used to chart every visible waterway and track how waste moves from streets to sea. These real-time insights guide optimal Interceptor placement and provide a public baseline against which progress can be measured.
Alongside intercepting new plastic, the 30 Cities Program will also remove debris from nearby coasts, mangroves, and coral reefs. This twin-track approach—shutting off the tap while clearing the legacy pollution—enables The Ocean Cleanup to achieve long-term impact, which includes the restoration of fish nursery habitats, boosting coastal tourism, and strengthening of natural storm surge defenses for local communities. Alongside local partners, the organization also advocates for improvements in waste management and awareness raising amongst communities.
Completing the First 20 Rivers
While laying the foundation for the 30 Cities Program, The Ocean Cleanup is also nearing completion of its first 20 river projects. The next landmark achievement—expected as soon as the second half of this year—is in the western Caribbean, where the team aims to resolve the plastic pollution problem in the Gulf of Honduras by intercepting the trash feeding into this body of water.
A Stepping Stone Toward a 90 Percent Reduction
The 30 Cities Program represents the first major scaling step in The Ocean Cleanup’s journey to eliminate 90 percent of floating ocean plastic pollution. In parallel, efforts are continuing to remove plastic from the Great Pacific Garbage Patch. Whilst extraction operations are currently on hiatus, work to deploy cutting edge technologies to map the “hotspots”, or areas of intense plastic accumulation, in order to make future extractions more efficient and economical, is ongoing.
By combining river interception and coastal cleanup with its offshore cleanup systems targeting legacy pollution that’s already in the ocean, the organization is charting a path to turn off the tap and mop up the mess.
About The Ocean Cleanup
The Ocean Cleanup is a nonprofit organization that develops and scales technologies to rid the oceans of plastic. By conducting extensive research, engineering scalable solutions, and partnering with governments, industry, and like-minded organizations, The Ocean Cleanup is working to stop plastic inflow via rivers and remove legacy plastic already polluting the oceans. As of June 2025, the non-profit has collected over 28 million kilograms (62 million pounds) of trash from aquatic ecosystems around the world. Founded in 2013 by Boyan Slat, The Ocean Cleanup now employs a multi-disciplined team of approximately 200 people. The organization is headquartered in Rotterdam, the Netherlands, with international operations in 10 countries. For more information, visit www.theoceancleanup.com.
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