A blue crab, a highly invasive alien species, is seen at Lio Piccolo during the reforestation day on April 05, 2025 in Venice, Italy. The island of Lio Piccolo in the northern lagoon of Venice is being replanted with 16,000 new trees that will protect the salt marsh ecosystem that is fundamental to the natural health of Venice and the lagoon by WOWnature project, an Etifor initiative. (Photo by Simone Padovani/Getty Images)

In this picture taken on Thursday, December 1, 2016, an Iranian woman covers herself with a blanket due to the cold, while visiting Khour salt lake during her tour of the Mesr desert about 305 miles (500 kilometers) southeast of the capital Tehran, Iran. Deserts make up parts of Iran which have recently become tourist destination for young Iranians looking for a break on their weekend. The increase in tourists to the desert has stimulated economic growth in the area. (Photo by Ebrahim Noroozi/AP Photo)

Dan McManus and his service dog Shadow hang glide together outside Salt Lake City, Utah, July 22, 2013. McManus suffers from anxiety and Shadow's presence and companionship help him to manage the symptoms. The two have been flying together for about nine years with a specially made harness for Shadow. (Photo by Jim Urquhart/Reuters)

A field of poppies in flower in Great Massingham, Norfolk, UK on Tuesday, June 25, 2024. The field has been rewilded by the landowner, with the soil being ploughed and harrowed before being left for nature to run its course with the result being a huge sea of red poppies. (Photo by Joe Giddens/PA Images via Getty Images)

Cars drive on an alley between rape fields in the outskirts of Frankfurt, Germany, Monday, April 22, 2024. (Photo by Michael Probst/AP Photo)

Women pose for a selfie in a lavender field at Hitchin Lavender farm in Ickleford, Britain, August 4, 2020. (Photo by Peter Cziborra/Reuters)

A cenote is a natural phenomenon, a sinkhole in the Earth’s surface. The Yucatan Peninsula in Mexico has an estimated 7,000 cenotes because it is primarily made up of porous limestone. For millions of years, rainfall slowly ate away at the limestone and a huge system of underground caves and caverns was formed. Many filled with water from rain or from the underground water table. When the roof of a water filled cave collapses, a cenote is born. The water found in a cenote may be fresh water, salt water, or both. Structurally it may be completely open, like a lake, almost completely closed with just a small opening at the top, or somewhere in between.