Divers Reveal More Secrets About the World's Longest Underwater Cave in Yucatan Peninsula

Cave divers from the Great Maya Aquifer Project explore Sac Actun. Karla Ortega/GAM

Researchers in Mexico who discovered the world's longest underwater cave are sharing more information about their incredible find.

In January 2018, the Underwater Exploration Group of the Great Maya Aquifer Project (GAM) found a connection between two of the world's largest flooded cave systems — Sac Actun and Dos Ojos — located in the Yucatán Peninsula. At 215.6 miles, the linked systems now form the longest known flooded cave.

"This immense cave represents the most important submerged archaeological site in the world, as it has more than a hundred archaeological contexts. Along this system, we had documented evidence of the first settlers of America, as well as extinct fauna and, of course, the Mayan culture," said Guillermo de Anda, researcher at the National Institute of Anthropology and History and GAM director, in a statement in January.

In this video, shot by Brian Wiederspan/Jeanna Edgerton (GAM)/@proyectogam, divers explore the cave system:

The researchers presented their findings at a press conference in late February. They found the remains of humans and animals, as well as artifacts, including ceramics and wall etchings. Among the animal bones were the fossils of gomphotheres — an extinct elephant-like animal — as well as giant sloths and bears, according to Phys.org.

Remains of a mask found in the Sac Actun underwater cave.
Remains of a mask found in the Sac Actun underwater cave. Archivo Gran Acuifero Maya

The team found relics including a shrine to the Mayan god of war and commerce, with a staircase that was reached via a sinkhole in the middle of the jungle.

staircase in jungle leading to Mayan temple
Researchers found a Mayan structure in the jungle above the caves. Archivo Gran Acuifero Maya

"It is very unlikely that there is another site in the world with these characteristics. There is an impressive amount of archaeological artifacts inside, and the level of preservation is also impressive," said de Anda.

Years in the making

Although this phase of the project lasted 10 months, beginning in March 2017, GAM director of exploration Robert Schmittner had been searching for this connection for 14 years, gradually mapping new tunnels and galleries as he found them.

Before this, the Ox Bel Ha System was the longest at nearly 168 miles; the Sac Actun System was second at 163 miles. Third is the KooX Baal System at 58 miles and fourth is the Dos Ojos System, with 52 miles. This last one is now part of the Sac Actun System.

According to caving rules, when two systems are connected, the largest cave absorbs the smallest and the name of the latter disappears.

The finding is also valuable because the cave supports wide biodiversity due to all the fresh water. According to the statement, "This aquifer, had given life to this region of the Yucatan Peninsula, from ancestral times, to the present day."