A close up of ornaments of centuries-old idols of Lord Buddha during the Pancha Daan, Five donation, festival in Bhaktapur, Nepal, 30 August 2016. Thousands of Buddhist pilgrims observe the main day of the Pancha Daan also known as a five summer gifts (rice, grain, salt, money and fruits) festival which is observes for world peace and human welfare. (Photo by Narendra Shrestha/EPA)

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.

Giant panda Jia Jia enjoys her birthday cake made with ice and vegetables at Ocean Park in Hong Kong, Tuesday, July 28, 2015 as she celebrates her 37-year-old birthday. Jia Jia broke the Guinness World Records title for “Oldest Panda Living in Captivity” on Tuesday. (Photo by Kin Cheung/AP Photo)

Birds congregate by the ocean at sunrise, after California’s governor said he would impose some of the nation’s strictest stay-at-home orders in the coming days, as the global outbreak of the coronavirus disease (COVID-19) continues, in Santa Monica, California, U.S., December 4, 2020. (Photo by Lucy Nicholson/Reuters)

This picture taken on May 4, 2020 shows a gentoo penguin swimming in an enclosure at the Ocean Park theme park, which is currently closed due to the COVID-19 novel coronavirus, in Hong Kong. (Photo by Richard A. Brooks/AFP Photo)

People pose for a photo with certificates after swimming in the ocean for the 121st annual Coney Island Polar Bear Club's New Year's Day plunge at Coney Island beach in the Brooklyn borough of New York, New York, USA, 01 January 2024. (Photo by Sarah Yenesel/EPA)

A dog named Izzy licks its chops as Craig Morland of Crofton, Maryland, buys a bucket of Thrashers famous fries on the first day of eased coronavirus disease (COVID-19) restrictions for the beach and boardwalk in Ocean City, Maryland, U.S., May 9, 2020. (Photo by Kevin Lamarque/Reuters)

The Predator’s Fins: Atho Ullah, Indonesia. 3rd place, Portfolio category. A freshly caught shark is taken ashore. Efforts to regulate shark fishing in Indonesia are not effective enough. Lack of awareness of the role sharks play in the ocean’s ecosystem poses a major threat to marine life. (Photo by Atho Ullah/2020 Hamdan International Photography Award)