SSI x Edges of Earth: We Dived The World’s Deepest Blue Hole In Chetumal, Mexico
September 4, 2024
It is tempting to believe that we have already uncovered everything there is to know about our planet, especially in the digital age. After all, the earth has been mapped out in painstaking detail via satellite. Some might even say the bygone era of "exploration," has been replaced by the encyclopedic depths of Google Maps. However, the truth is far from it, as proved by the recent discovery of the world’s deepest blue hole!
With only 20% of the ocean explored and more than half of the planet’s surface still a mystery, there are still vast expanses waiting to be discovered.
It is why encountering new and astonishing phenomena in the ocean should not be seen as unusual, but rather anticipated. We are barely scratching the surface of what we know! So when we learned that local fishermen, along with the help of a research center, had discovered what was now dubbed the world’s deepest blue hole in 2024, we were ecstatic—and eager to connect. Initially, we imagined this blue hole would be far offshore, akin to Belize’s Great Blue Hole. Yet, to our surprise, it was located in Chetumal Bay, remarkably close to mainland Mexico.
Why has the world’s deepest blue hole only just been discovered?
Driven by curiosity and eager for answers, we contacted the scientist behind the groundbreaking research paper we had found, Dr. Juan Carlos Alcérreca Huerta. Much to our surprise, there had been no media coverage of this remarkable discovery at the time. In fact, it took considerable effort to uncover his paper ourselves. We just happened to be in the right place, at the right time, looking right at Juan Carlos’ location on a map upon the release of this paper. We were certain that it was only a matter of time before others, just as intrigued as we were, started asking the same burning question:
How did the world’s deepest blue hole remain unknown until now?
But before we answer that question, I must tell you more about the man behind the discovery itself, Juan Carlos. Upon meeting, we realized we could have talked to him forever about the topic. His passion was obvious, and he eagerly wanted us to meet the entire ECOSUR Research Center team involved in this work. By the way, El Colegio de la Frontera Sur (ECOSUR) is one of the foremost research institutions in southeast Mexico, with a presence in all states along the borders of Guatemala and Belize!
At the time of our first call, Juan Carlos knew they found something special, but they had not fully confirmed that their discovery was the world’s deepest blue hole. However, as we rearranged our plans and put Chetumal, Mexico on our expedition trail, the news became official:
Taam Ja’, a 425-meter blue hole, surpasses China’s Dragon Hole, which previously held the title of the world’s deepest blue hole at 301 meters.
Getting to Chetumal was a straightforward journey for us because we were already in Belize wrapping up our Central American trek by car. Our plan from there was to drive up the Yucatan Peninsula, and Chetumal happened to sit right on the border of Belize and Mexico. Crossing the Belize-Mexico border was a familiar task, despite the expected crossing delays—we had already navigated five previous border crossings by car, so we considered ourselves pros at this point. Now, we just had to make it to Chetumal. But, before we could do that, we had to do the long drive down to Mahahual, a small village about 2.5 hours away by car, to retrieve scuba tanks.
Chetumal is far away from your typical dive destinations so there were not any tanks available in the city. This location is not pulling in international visitors like some other places that have put diving in Yucatan on the map. And we were about to find out why. However, moving south along the Quintana Roo coast, from Mahahual down to Xcalak near the Belize border, there is fantastic diving along the Meso-American Barrier Reef. Curious to explore the entire stretch, we decided to drive down past Mahahual to Xcalak, the southernmost tip, to experience the diving there as well.
Another unexpected find during our research journey was Playa Sonrisa, where we stayed in Xcalak. It turned out to be a haven for naturalists—a small community we had known nothing about until then. Here, people embrace nudity as a way to connect more intimately with nature, drawing visitors from around the globe who seek places that support this lifestyle. The property itself was stunning, with an SSI dive center, Playa Sonrisa Dive, on site. Unfortunately, the ocean conditions were less than ideal. With rough seas and poor visibility, we opted to stay on land the week before our expedition stop in Chetumal, removing ourselves from the salty life. From there, we took the dirt road out of remote Xcalak, hit Mahahual, picked up our tanks, and touched down in the Chetumal Bay area—it was time to explore the world’s deepest blue hole.
Chetumal was exactly as we expected: a regional, yet commercial center. We were not necessarily there to "check out the sights." We were there to go deep—really deep. Upon our arrival, the study of the blue hole had been limited to its depth, salinity, density, and the composition of its accessible points. Many questions remained unanswered, with the biggest one lingering in our minds: how had the world’s deepest blue hole eluded detection for so long?
The answer has to do with the fundamental properties of the bay itself. Unlike Belize’s Great Blue Hole (which is visible by satellite even from space), drones are even unable to spot this blue hole from directly overhead! This is because the conditions in the bay were far too rough, with murky waters and choppy waves obscuring any view. Simply put, Taam Ja’ is completely concealed by the bay’s challenging conditions. Even on the best days, visibility is limited, and for us, the surface water was far from optimal.
When the day arrived for our expedition into the bay, we were introduced to Dr. Óscar F. Reyes-Mendoza. Óscar, a seasoned scientist and diver, had explored Quintana Roo’s underwater world extensively. His early career included whale shark research around Playa Del Carmen, and his underwater tales were nothing short of epic. Alongside him was Jesús Artemio Poot-Villa, the fly fisherman who, along with his father, had stumbled upon the blue hole TWENTY YEARS AGO.
Yes, you read that right—they had known about this blue hole for two whole decades.
Jesús’ father discovered the blue hole while fishing, but he did not think much of it because there were no fish in the hole (now understood because of the lack of oxygen). Years later, when Juan Carlos conducted a survey of Chetumal Bay via ECOSUR Research Center, he collaborated closely with Jesús, who, aware of the local environment from growing up on the bay, asked Juan Carlos if he wanted to see something surprising that had been right under their noses.
Juan Carlos, originally trained as a civil engineer, had never planned to become a marine scientist and does not know how to swim, nor does he have any interest in learning. However, his fascination with the complexity of the coastal environments and what he was discovering in Chetumal led him to fall in love with marine science. So, we set out without him, with Jesús guiding us and Óscar providing moral support.
We were going to venture alone into the world’s deepest blue hole - a place that had been dived by only six people before us.
Óscar’s briefing was simple: we would anchor near the south side of the blue hole, avoiding the aggressive conditions of the north side that day. Our descent would begin around the rim, where visibility would be nil for the first five meters. Upon breaking through the pycnocline, where water density shifts, we would encounter crystal-clear water, a nearly vertical limestone drop-off at an 80-degree angle, and the opportunity to explore for as long as we could. We would experience abrupt changes in water temperature (thermocline) and salinity (halocline). With our maximum depth left to our discretion, we opted for safety at 45.5 meters. With these completely unexplored waters, we were diving into quite literally, the unknown.
Equipped with our scuba gear, Marla and I descended while Adam and his father opted to go freediving. The initial foggy five meters were disorienting, but once we reached the rim, we were spellbound: nothing had prepared us for this sight. This vast blue hole stretched out 152 meters wide on its longest axis. It was serene, yet thrilling, with its clear waters shifting from warm to cold in an instant. The stillness was surreal, leaving us feeling like we were not even underwater at all. Marla and I began our descent practically hand-in-hand, exchanging amazed glances the deeper we went.
We observed how the walls of the blue hole would subtly shift if we approached them, a phenomenon Juan Carlos attributed to a mixture of biofilms, sediment, and irregular rocky surfaces lining the walls, some reaching 2-3 meters in height. These surfaces were adorned with a thin layer, likely gypsum, and covered in easily dislodged brown, red, and black algae and bacteria mats. Sections of exposed white limestone suggested recent rock falls. Floating or attached to the walls were slimy filaments up to a meter long, reminiscent of those found in oxygen-depleted blue holes. Benthic fauna, such as small worms and barnacles, clustered primarily in the first 5-10 meters, while no pelagic life was observed.
We felt like the blue hole itself—or "poza" as Jesús called it—was breathing, the formation itself seemed as if it was alive.
Amidst the thick of this untouched paradise, we contemplated its implications for science, conservation, and tourism in Chetumal’s future. Jesús welcomed the discovery, hopeful it would attract attention to Chetumal and boost fly fishing tourism. However, as we descended to 45.5 meters, where light faded almost completely, we agreed that this was far from your typical tourist destination. Even at a mere 15 -20 meters below sea level, detritus particles reduced visibility, solidifying our belief that this, the world’s deepest blue hole, was more suited for science and science alone.
Surfacing from our first dive, we screamed, we cheered, and we held each other in the water. It was truly an incredible discovery that we were honored to be a part of.
It was an exciting, terrifying, and temperamental dive all at the same time. It was honestly flat-out confusing! We understand now the who, what, when, where, and why of it all, and what was next for Juan Carlos and his colleagues and collaborators. They were now going to take their first round of research and proceed to the next level, learning more and more about what this means for the region, the country, and more broadly, blue hole science.
Following our dives, we met with Dra. Laura Carrillo, Dra. Teresa Álvarez-Legorreta, Dr. Joan A. Sánchez-Sánchez, MSc Laura María Flórez-Franco, and MSc Johnny Valdés, all integral to the exploration, research, and recent mapping of the blue hole. Each conversation echoed a shared sentiment of pride in being part of this historic moment in Chetumal alongside Jesús and his family. They were all eager to advance their scientific inquiry, exploring the true depth of the hole (beyond the 425-meter mark reached by their current instruments).
They seek to further understand the blue hole’s potential underwater connections, unraveling the mysteries of its deeper layers, and uncovering any other radical discoveries that come along the way. And we signed up to be part of the team to help share whatever it is they uncover next!
Where can you go diving in blue holes?
Are you fascinated by blue holes? There are blue holes worldwide that offer unique scuba diving and freediving experiences. Check out these popular blue holes to inspire your next dive trip:
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Andi Cross is an SSI Ambassador and lead of the Edges of Earth expedition, highlighting stories of positive ocean progress and how to explore the world more consciously. To keep up with the expedition, follow the team on Instagram, LinkedIn, TikTok, YouTube, and their website.