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.

Emperor penguins gathered together to keep their chicks warm in these pictures. Marine scientist Frederique Oliver snapped the protective parents in Antarctica as they huddled against the huge winds.The adorable birds have to battle temperatures on -20 degrees Celsius as well as winds of up to 40 knots on the ice. (Photo by Frederique Oliver/Caters News)

On the second straight day of record-setting temperatures, Maddy Hacker is hoisted up by friend Jasmine Harper, both of McLean, Virgnia, as they attempt an acrobatic stunt in front of the U.S. Capitol in Washington, U.S., February 21, 2018. (Photo by Kevin Lamarque/Reuters)

A model is seen backstage before the Manish Arora Spring/Summer 2019 women's ready-to-wear collection show during Paris Fashion Week in Paris, France, September 27, 2018. (Photo by Stephane Mahe/Reuters)

A squatter argues with a police officer during an eviction at a settlement coined the “First of May Refugee Camp”, named for the date people moved on the land designated for a Petrobras refinery, in Itaguai, Rio de Janeiro state, Brazil, Thursday, July 1, 2021, amid the new coronavirus pandemic. (Photo by Silvia Izquierdo/AP Photo)

Belgian yoga teacher Dorien Dierckx, 29 from Brussels enjoys a beer while relaxing in a jacuzzi full of hot water and a mixture of ingredients used to make beer, and where customers can serve their own beer from the tap at the Good Beer Spa in Brussels, Belgium on May 12, 2021. (Photo by Yves Herman/Reuters)

A policeman jumps as he tried to avoid a tear gas grenade thrown back towards police by protesters in the Mathare neighborhood of Nairobi, Kenya Wednesday, July 12, 2023. Kenyans angered by the rising cost of living were back protesting on the streets of the capital, Nairobi, on Wednesday, as they awaited a speech by a longtime opposition leader. (Photo by AP Photo/Stringer)