Split-view of a killer whale at sunrise off the coast of Northern Norway. At least half of the world’s killer whale populations are doomed to extinction due to pollution of the oceans, a new study says. (Photo by Audun Rikardsen/Science)

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.

An activist kicks the shields of the military police officers during a demonstration in the military zone of the 27th infantry battalion in Iguala, Guerrero, January 12, 2015. Activists and relatives of the 43 missing trainee teachers from Ayotzinapa's teacher training college broke into the military zone, located less than a mile from where the students went missing, in an attempt to look for the missing students.The remains of only one of the 43 students has been identified so far. (Photo by Jorge Dan Lopez/Reuters)

March 11, 2008 Swiss car manufacturer Rinspeed made quite the splash at the Geneva Motor Show with its innovative sQuba, a fully functional submersible concept car that cost $1.5 million to build. (Photo by Rinspeed)

Ginger Stanley performs a grand jete during her solo underwater ballet at Silver Springs, Florida. (Photo by Bruce Mozert/Three Lions/Getty Images). Circa 1956

The artist Samantha French reveals the magnificent series of paintings: portraits of men and women under water. Very realistic creations expressing the world under water. Every detail is present, sunlight on water, air bubbles in the water, the color tone underwater, aquatic atmosphere. Absolutely amazing to discover in the rest of the article works.

“Emmy” award-winning cinematographer, Shawn Heinrichs teamed up with model and diver Hannah Fraser to carry out a unique underwater conservation fashion shoot in a remote location in the South Pacific Ocean. The pair are aiming to raise awareness for the plight of the marine mammals at the hands of whalers. During the ten day shoot Fraser swam and glided with pilot and humpback whales. Photo: “In this startling image model Hannah Fraser appears to be “dancing” with the giant whale ”. (Photo by Shawn Heinrichs/Barcroft Media)

A woman dives and pretends to ride a bike in Underwater Park in Pula, Croatia, August 1, 2017. (Photo by Antonio Bronic/Reuters)