A Kashmiri Muslim woman balances on a water pipe before collecting water at Dasilpora village on March 22, 2018. World Water Day is held annually on 22 March as a means of focusing attention on the importance of freshwater and advocating for the sustainable management of freshwater resources. (Photo by Tauseef Mustafa/AFP Photo)

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 child falls sleep while people take part in the 35th India Day Parade in New York August 16, 2015. (Photo by Eduardo Munoz/Reuters)

A visitor falls down as they run away from a wave caused by a tidal bore which surged past a barrier on the banks of Qiantang River, in Hangzhou, Zhejiang province, China, October 28, 2015. (Photo by Reuters/China Daily)

A young protester takes part in a protest near Tahrir Square to call for the fall of Islamist President on January 24, 2012 in Cairo. (Photo by Mohammed Abed/AFP Photo via The Atlantic)

Model Winnie Harlow wears a creation as part of the John Richmond men's Fall-Winter 2019-20 collection, that was presented in Milan, Italy, Sunday, January 13, 2019. (Photo by Antonio Calanni/AP Photo)

A model presents a creation by Andrea Crews as part of their Fall/Winter 2019-2020 collection show during Men's Fashion Week in Paris, France, January 19, 2019. (Photo by Gonzalo Fuentes/Reuters)

A model presents a creation by Givenchy during men's Fashion Week for the Fall/Winter 2017/2018 collection in Paris on January 20, 2017. (Photo by Patrick Kovarik/AFP Photo)