The Cave Guardian: What Drives Roberto Rojo Underground

Speleologist documents the world beneath Yucatán—and fights to protect it from destruction

Roberto Rojo was 30 meters underground when the drilling started. Stalactites that had formed over millennia began tumbling around him as a massive industrial drill punched through the limestone ceiling above. The biologist ducked for cover, phone in hand, recording what would become some of the most dramatic footage of environmental destruction in Mexico’s recent history.

“It was our worst nightmare,” Rojo says, standing beside one of the 40 steel columns now marching through that same cenote in rows of four. “We’ve seen a large drill entering and breaking the ceiling of the cave, destroying ancient stalactites that took thousands of years to form.”

The 45-year-old speleologist has spent two decades exploring the underground cave systems that honeycomb the Yucatán Peninsula. What began as scientific curiosity about Mexico’s tarantula species has evolved into a mission to document and preserve one of the world’s most extensive underwater cave networks—a 64,000-square-mile aquifer that supplies the only source of freshwater to millions of people across the region.

Rojo’s path to becoming one of Mexico’s most visible environmental activists started at UNAM, where he earned his biology degree before completing graduate studies at El Colegio de la Frontera Sur. His early research focused on arachnids, particularly the endangered Mexican redrump tarantula, Brachypelma vagans. That work led him deep into Yucatán’s jungles and caves, where he discovered an entire hidden ecosystem.

“I’ve worked with crocodiles, sea turtles, jaguars, pumas, ocelots,” he says, listing decades of fieldwork across Yucatán’s diverse ecosystems. “But the cenotes became my passion because they connect everything. Every plant, animal, and person in this region depends on them.”

His expertise earned him a role as host of scientific television programs on Canal Once, the National Polytechnic Institute’s educational channel. He’s given more than 100 lectures across 15 Mexican states and five countries. He’s published two books on Mexico’s underground world with Editorial NOSTRA. But it wasn’t until 2020, when construction began on the Tren Maya railway, that Rojo transformed from scientist to activist.

The $30 billion project opened fully in December 2024. It required driving an estimated 15,000 steel pillars into the ground to support elevated sections of track across the peninsula. Many of those pillars punched directly through cave ceilings, contaminating cenotes with cement and rust. Rojo co-founded two organizations to fight the project: Selvame del Tren (Save Me From the Train) and Cenotes Urbanos, which focuses on cleanup efforts and community education.

Mexico’s environmental protection agency documented at least five concrete spillages linked to the railway construction. The spills occurred in cenotes that serve as drinking water sources for local communities and eventually reach the Mesoamerican Reef, the world’s second-largest coral reef system.

“Everyone is connected through the cenotes,” says José “Pepe” Urbina, a veteran cave diver who works with Rojo to map the underground damage. “That’s what makes Roberto’s work so important. He’s documenting threats to the foundation of life on the peninsula.”

The scale of that threat became clear as Rojo and his team explored contaminated cenotes. In one cave near Playa del Carmen, they found cement spills that had created dark stains across previously crystal-clear water. In others, they discovered rust flakes shedding from pillars into pools that serve as drinking water sources for nearby communities. Some cenotes have been turned into illegal dumping grounds, forcing Rojo and volunteers to extract everything from beer bottles to printers from underwater caves.

The work has drawn criticism from government officials. Former President López Obrador called members of Selvame del Tren “pseudo-environmentalists” and accused them of profiting from “alleged defense of nature.” The construction work was declared a matter of “national security,” placing it under military protection.

“Reaching some of the damaged cenotes requires driving several kilometers from Playa del Carmen, then hiking through jungle with a machete,” Rojo explains. “Once inside, you need a helmet with a flashlight. These aren’t tourist cenotes—they’re remote, fragile ecosystems that have been left contaminated and abandoned.”

The confrontation has taken a personal toll. Rojo knows that speaking out against a government megaproject carries risks. His scientific training helps him document the damage methodically, providing evidence that has appeared in National Geographic and other international media. Local coverage has also tracked the ongoing environmental impact as the project’s effects become clearer.

Despite the conflict over Tren Maya, Rojo continues his original research. His work documenting how Chol Maya communities use tarantulas in traditional medicine represents a bridge between indigenous knowledge and modern science. He’s found that Mayan healers have developed sophisticated understanding of arachnid biology, knowledge that could inform conservation efforts for endangered species.

“The Maya have always understood that everything is connected,” Rojo says. “The cenotes, the forest, the animals, the people—it’s all one system. When you damage one part, you damage everything.”

That interconnectedness drives his current work with Cenotes Urbanos, which organizes regular cleanup efforts while educating communities about the cenotes’ ecological importance. The organization has removed tons of garbage from underwater caves while documenting the spread of contamination across the peninsula’s aquifer system.

At least 8,000 cenotes are registered across Mexico’s Yucatán Peninsula, though the actual number may be much higher since sinkholes can appear suddenly as limestone gives way to centuries of erosion. Cave divers have mapped roughly 900 miles (1,448 kilometers) of underwater caverns, but experts estimate this represents only 10 percent of the total system.

As development pressure continues across Yucatán, Rojo and his colleagues are racing to catalog what remains. Some caves may contain Maya artifacts that have sat undisturbed for centuries. Others harbor endemic species found nowhere else on Earth.

“I trust that there are solutions,” Rojo says, standing in the filtered sunlight that illuminates a cenote entrance. “But it may take generations to undo the damage we’re seeing now. That’s why documenting everything is so important. We’re creating a record of what existed.”

For now, he continues descending into Yucatán’s underground world, camera in hand, bearing witness to both destruction and wonder in the caves beneath Mexico’s most famous tourist destination.

Sources: National Geographic, France24, Academia.edu, Earth Journalism Network, Digital Journal, iNaturalist Mexico, VOA News