History of cenote exploration

Before exploration: the Maya and earlier people

Nobody 'discovered' cenotes. People were using them more than 10,000 years ago, when many caves were still dry; the skeleton nicknamed Naia, found in the flooded Hoyo Negro pit in Sac Actun, is reported to be about 12,000 to 13,000 years old. The Maya later built cities such as Chichén Itzá and Mayapán next to cenotes, used them for water and treated some as sacred doors to the underworld (Xibalba).

Spanish accounts (1500s)

Bishop Diego de Landa wrote in the 1560s that the Maya threw offerings and people into the Sacred Cenote at Chichén Itzá in times of drought. His account, written while he was also destroying Maya books, inspired later treasure hunters.

Edward Thompson dredges the Sacred Cenote (1904–1910)

American consul Edward H. Thompson bought the hacienda around Chichén Itzá and dredged the Sacred Cenote with a bucket dredge, later diving it himself in a heavy helmet suit. He pulled up gold, jade, copal incense, pottery and human bones and sent many pieces to Harvard's Peabody Museum. Mexico later sued, and some objects were returned decades later (reported).

Scuba archaeology (1960s)

• 1960–61: a Mexican and American team with the National Geographic Society worked in the Sacred Cenote using an airlift (reported).
• 1967–68: Mexico's INAH partly drained and chemically cleared the water to recover more offerings (reported).
• Finds included thousands of artifacts and the remains of over 100 people (reported), many of them children.

Cave divers map the Tulum caves (1980s–2000s)

• Divers began pushing into the flooded caves of Quintana Roo in the 1980s, laying guidelines and mapping by hand.
• Dos Ojos and Nohoch Nah Chich became famous as some of the longest underwater caves known.
• The Quintana Roo Speleological Survey (QRSS) began keeping public records of cave lengths.
• 2007: divers found Hoyo Negro, a deep pit full of Ice Age animal bones and the Naia skeleton (reported).

Record depths and connections

• El Zacatón (Tamaulipas): in 2007 a NASA-backed robot, DEPTHX, measured it at over 300 m deep (reported).
• 2018: the Gran Acuífero Maya project announced that Sac Actun and Dos Ojos connect, making Sac Actun the world's longest known underwater cave at about 347 km at the time (reported).
• Diver Jim Bowden reached about 282 m in Zacatón in 1994 (reported).

Who explores cenotes today

• Volunteer cave divers and groups like QRSS and the Gran Acuífero Maya (GAM) project.
• Mexico's INAH, which protects archaeological finds underwater.
• Universities studying the aquifer, cave life and climate records in cave rock.
• Local communities who find and open new cenotes for visitors.

What exploration has revealed

Cenotes are now known as time capsules: Ice Age animal bones, some of the oldest human remains in the Americas, Maya offerings, and records of past climate in cave formations. Exploration also showed how fragile the aquifer is, which drives today's conservation work.