The World’s Longest Underwater Cave Has Been Discovered

Take a really, really deep breath.

A watery underworld stretching for 347 kilometres has been found beneath Mexico’s Yucatán Peninsula.

Divers from the Gran Acuifero Maya (Great Mayan Aquifer) project have been probing the submerged limestone labyrinths of the Sac Actun (263 kilometres) and Dos Ojos (83 kilometres) cave systems to determine if they connected.

Longest Underwater Cave in the World Discovered in Mexico

After 10 months of exploration, they confirmed the two caverns do in fact link up, creating what is thought to be the world’s longest underwater cave system. Sac Actun now absorbs the smaller cave, as per the rules of caving.

The scale of the twisting tunnel near popular resort town Tulum is truly staggering: 347 kilometres is the equivalent of driving halfway to Adelaide from Melbourne. With a maximum depth of 101 metres, the system is a mix of cavernous passages lined with stalactites and narrow channels barely big enough for a human to squeeze through.

Researchers and divers from the project believe this discovery will provide greater insights into the Maya people who once dominated the region, particularly around sites of religious significance. Religious objects and bones have previously been found at the bottom of other cenotes – underwater sinkholes – in Mexico.

But it’s just one of hundreds of other fascinating, winding cave systems in the Quintana Roo region. There are 358 other submerged caves systems in the area, including the 270-kilometre Ox Bel Ha System, which previously held the title of the world’s longest.

Divers are already onto their next project: determining whether Sac Actun also connects with another three nearby cave systems.

Image credits: anjči (CC BY 2.0), courtesy Cenotes Sac Actun.