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.

A porter stands at the bottom of the Illimani mountain, on the outskirts of La Paz, Bolivia, April 16, 2016. For years, Lydia Huayllas, 48, has worked as a cook at base camps and mountain-climbing refuges on the steep, glacial slopes of Huayna Potosi, a 19,974-foot (6,088-meter) Andean peak outside of La Paz, Bolivia. But two years ago, she and 10 other Aymara indigenous women, ages 42 to 50, who also worked as porters and cooks for mountaineers, put on crampons – spikes fixed to a boot for climbing – under their wide traditional skirts and started to do their own climbing. (Photo by David Mercado/Reuters)

In this Monday, September 22, 2014 photo provided by the Utah Division of Wildlife Resources, a young cougar is released back into Utah's mountains by the Utah Division of Wildlife Resources in an undisclosed site in central Utah. State wildlife officials received reports of the cougar roaming Sunday afternoon in a residential area of the city's eastern flank, a few miles from the base of the Wasatch Mountains. Authorities say cougars generally avoid humans but sometimes enter neighborhoods close to their mountain habitats. (Photo by Steve Gray/AP Photo/Utah Division of Wildlife Resources)

Alexandra Mazo, 12, with her cellphone on her way down the mountain after finishing school. The remote mountain village of Pueblo Nuevo has been highly affected by the armed conflict and direct combat between the national army and Farc guerrillas due to its strategic location and the intensive production on coca crops on the surrounding hillsides. (Photo by Mads Nissen/Politiken/The Guardian/Panos Pictures/The Nobel Peace Center)

In this photo taken October 12, 2019, a spiritual healer known as a “madrina” starts a ritual on Sorte Mountain where followers of indigenous goddess Maria Lionza gather annually in Venezuela's Yaracuy state. While her followers gather on the mountain for weeks at this time of the year, October 12 marks the biggest gathering, coinciding with Indigenous People's Day, known in Latin America as “Dia de la Raza”. (Photo by Ariana Cubillos/AP Photo)

A girl carries utensils after filling them with water from a pipe that supplies water to trains at a railway station on the outskirts of Agartala, India, February 28, 2017. (Photo by Jayanta Dey/Reuters)

Ukrainians pour water on each other on a street in Lviv, Ukraine, 02 May 2016. The tradition of pouring water was an ancient spring ritual of cleansing on first Monday after Orthodox Easter. (Photo by Mykola Tys/EPA)

Boys play with water as they celebrate Myanmar's New Year Water Festival of Thingyan in Yangon, April 13, 2016. (Photo by Soe Zeya Tun/Reuters)