Kalei Ferrin,3, holds a sign up in support of gay rights during the San Diego gay pride parade July 16, 2011 in San Diego, California. About 200 active-duty troops and veterans from every branch of the military participated for the first time in the march as the ban on the government policy on homosexuals serving in armed forces, or “Don't ask Don't Tell”, remains in flux in the justice system. (Photo by Sandy Huffaker/Getty Images)

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.

School children celebrate after being rewarded for their dance performance during India's Independence Day celebrations in Chandigarh, India, August 15, 2015. Indian Prime Minister Narendra Modi's independence day speech focused on measures his “Team India” had rolled out to include millions of poor Indians in the banking and insurance systems, policies for workers and farmers and successes in the fights against inflation and corruption. (Photo by Ajay Verma/Reuters)

A handout picture made available by the National Aeronautics and Space Administration (NASA) shows, NASA teams working around Boeing’s CST-100 Starliner spacecraft after it landed at White Sands Missile Range’s Space Harbor, in Las Cruces, New Mexico, 25 May 2022. Boeing’s Orbital Flight Test-2 (OFT-2) is Starliner’s second uncrewed flight test to the International Space Station as part of NASA's Commercial Crew Program. OFT-2 serves as an end-to-end test of the system's capabilities. (Photo by Bill Ingalls/NASA/EPA/EFE)

Palestinian groom Mohamed abu Daga and his bride Israa wear face masks amid the COVID-19 epidemic, during a photoshoot at a studio before their wedding ceremony in Khan Yunis in the southern Gaza Strip, on March 23, 2020. Authorities in Gaza confirmed on March 22 the first two cases of novel coronavirus, identifying them as Palestinians who had travelled to Pakistan and were being held in quarantine since their return, as the United Nations warned of potential disastrous outcomes to an outbreak given the high poverty rates and weak health system in the coastal strip, under Israeli blockade since 2007. (Photo by Said Khatib/AFP Photo)

Igor Shpilenok works in the reserve at Kamchatka, Russia. Igor is a fellow of the International League of Conservation Photographers and a winner of the 2006 BBC Wildlife Photographer Competition. Igor’s work has been published in numerous international and Russian magazines, including Smithsonian, National Wildlife, Geo, and BBC Wildlife.

“How does a bear behave when encounter a human? In most cases he runs away. But before running he almost always would rise to stand on his rear feet. And this behavior does not indicate the attack, as many people think...” – Igor Shpilenok. (Photo by Igor Shpilenok via Wildlife Photo Russia)

One-month-old cubs given birth by giant panda “Su Shan” are seen at Shenshuping giant panda base on August 17, 2021 in Aba Tibetan and Qiang Autonomous Prefecture, Sichuan Province of China. (Photo by He Haiyang/VCG via Getty Images)

Biologists Jenna Cormany (L) and Lauryn Wright of the South Carolina Department of Natural Resources help to release a leatherback turtle in Isle of Palms, South Carolina March 12, 2015. The 475-pound turtle was the first living leatherback turtle to be recovered in South Carolina and one of only a handful ever treated at rehabilitation facilities in the United States. It was found March 7 on the beach on Yawkey-South Island Reserve, a 3.5-mile-long (5.6-km-long) barrier island and wildlife preserve near Georgetown, South Carolina. (Photo by Randall Hill/Reuters)