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.

Artist Le Pustra and organiser Else Edelstahl pose for a picture at Simon Dach Strasse, a street filled with many bars, in Berlin, Germany, August 28, 2016. Else Edelstahl organises the party series “Boheme Sauvage”, in which people dress up in 1920s style, celebrating Berlin nightlife of a past era. (Photo by Hannibal Hanschke/Reuters)

ABC's “Jimmy Kimmel Live” features a week of guest hosts filling in for Jimmy, starting Monday, October 30, 2017. The guest host for Thursday, November 2 was Jennifer Lawrence with guest Kim Kardashian West (KKW Beauty) and musical guest Linkin Bridge. (Randy Holmes/ABC via Getty Images)

A dog sits in a plastic basin filled with water in Taipei, Taiwan, 05 May 2018. Betel nut seller Mr Luo, the dog's owner, said he puts his dog Ah Dai (Stupid Guy) in the water-filled basin whenever the weather get hot. Luo has a dozen pairs of glasses for Ah Dai, so the dog wears different glasses every day and many tourists take photos of Ah Dai. (Photo by David Chang/EPA/EFE)

A worker fills a public bus with diesel as the bus driver and passengers look on, at a fuel station in Kolkata, India, February 1, 2017. (Photo by Rupak De Chowdhuri/Reuters)

Fishermen fill crates with sardines netted during the annual sardine run in Warner Beach, South Africa on June 3, 2025. (Photo by Rogan Ward/Reuters)

A pool ingeniously filled with clear water in the middle of Lake Kerniki in Greece enabled this shot of feeding pelicans. (Photo by Bence Mate/Close Up Photographer of the Year 2020)

Bristol celebrates “wonderful diversity” at St Paul's carnival on Saturday, July 6, 2019. Thousands filled the streets for the city’s 51st procession highlighting the contribution of the Windrush generation. (Photo by Alex Turner/The Guardian)