Zacatón, Water-filled sinkhole in Tamaulipas, Mexico

Zacatón is a water-filled sinkhole in the limestone bedrock of Tamaulipas, reaching 339 meters (1112 feet) into the earth. The opening at the surface measures roughly 116 meters (381 feet) across and leads into a nearly vertical chamber with steep walls dropping into deep blue water.

Félix María Calleja mentioned the sinkhole in official records in 1795 as viceroy of New Spain. In 2007, a robotic underwater vehicle descended to the bottom, providing the first complete measurement of the chamber depth and shape.

The name Zacatón comes from the free-floating islands of zacate grass that drift across the water with the wind. These rafts of vegetation shift position, so the open water and the grass-covered stretches change from one visit to the next.

Access requires permission from property owners, as the site sits on private land. Diving activities are limited to experienced professionals and scientific expeditions familiar with extreme depth conditions.

Researchers found three previously unknown bacterial groups living in the water in the extreme environment far below the surface. These microorganisms thrive in conditions with low light and high mineral content, expanding ideas about possible life in remote habitats.