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 tourist splashes water on the frozen Songhua River on December 18, 2023 in Harbin, Heilongjiang Province of China. The water immediately freezes into ice in the frigid air. (Photo by VCG/VCG via Getty Images)

A bucket of water is splashed on a woman during the Songkran water festival to celebrate the Thai New Year, in Prachinburi Province, Thailand, April 13, 2024. (Photo by Wason Wanichakorn/AP Photo)

Protestor Bill Maloney (L) shouts during a live TV broadcast by BBC News Channel chief political correspondent Norman Smith after earlier forcing Deputy Prime Minister Nick Clegg to abandon a photocall near Parliament on March 19, 2014 in London, England. The Chancellor of the Exchequer, George Osborne has delivered his Budget statement to Members of Parliament in the House of Commons. (Photo by Peter Macdiarmid/Getty Images)

Damai, 3 years old Bornean orang utan plays courtyard at Surabaya Zoo as he prepares to be released into the wild on May 19, 2014 in Surabaya, Indonesia. The two baby orangutans, brothers, were found in Kutai National Park in a critical condition having been abandoned by their mother on May 14, 2014. The Centre for Orangutan Protection (COP) have since been nursing the animals back to health, treating them for malnourishment and 16 wounds predominantly to the feet and hands. (Photo by Robertus Pudyanto/Getty Images)

Members of Brazil's Movimento dos Sem-Teto (Roofless Movement) stand in the hallway of one of the 11 empty buildings that the movement took over recently, in the centre of Sao Paulo, November 6, 2012. According to City Hall, there are some 400,000 people in need of stable housing, including the 4,000 families of the Roofless Movement who are squatting in abandoned or vacant buildings that range from apartment blocks to hotels, in Sao Paulo, the largest city in South America. (Photo by Nacho Doce/Reuters)

The 30th anniversary of the meltdown at the Chernobyl nuclear plant that caused large amounts of radioactive particles to be released into the air will be commemorated on April 26, 2016. Photojournalist Sean Gallup returned to the area to document the lasting effects of the world's worst nuclear power plant accident. Pictured, children's beds are seen in an abandoned kindergarten in Kopachi village located inside the Chernobyl exclusion zone, September 29, 2015, near Chernobyl, Ukraine. (Photo by Sean Gallup/Getty Images)

An abandoned tank left by Boko Haram, February 20, 2016, seen on the road to Michika, Nigeria – a town formerly occupied by the insurgents. On April 14, 2014, 300 schoolgirls in the Chibok village in Nigeria were kidnapped by the terrorist group, Boko Haram. Two years later, the majority of these girls are still missing. According to the Global Terrorism Index Report 2015, Boko Haram, which operates mainly in Nigeria, has become the most deadly terrorist group in the world. (Photo by Danielle Villasana)