A reef shell lies on a beach as the sun sets on Lady Elliot Island located north-east of the town of Bundaberg in Queensland, Australia, June 10, 2015. UNESCO World Heritage delegates recently snorkelled on Australia’s Great Barrier Reef, thousands of coral reefs, which stretch over 2,000 km off the northeast coast. Surrounded by manta rays, dolphins and reef sharks, their mission was to check the health of the world's largest living ecosystem, which brings in billions of dollars a year in tourism. Some coral has been badly damaged and animal species, including dugong and large green turtles, are threatened. UNESCO will say on Wednesday whether it will place the reef on a list of endangered World Heritage sites, a move the Australian government wants to avoid at all costs, having lobbied hard overseas. Earlier this year, UNESCO said the reef's outlook was “poor”. (Photo by David Gray/Reuters)

This photographer has made it her mission to change people’s perception of pigeons – focusing on some of the most beautiful of the more than 300 species found globally. Rather than focus on the gray, nondescript birds people usually associate with the term “pigeon”, Leila Jeffreys has instead decided to snap the more vibrant varieties. Whether it be the wompoo pigeon, with its deep purple breast and green wings, or the rose-crowned fruit dove, with its pink head, Jeffreys, 46, gives the birds the same attention she would give a human model. (Photo by Leila Jefferies/Caters News Agency)

People look on as water from the rising Mississippi River is released through the Bonnet Carre Spillway while washing out a road May 9, 2011 in Norco, Louisiana. The Army Corps of Engineers began redirecting part of the Mississippi River through the spillway today to lower river levels and reduce pressure on levees in order to avoid a catastrophic failure. The water will flow nearly 6 miles north before emptying into Lake Pontchartrain as the Mississippi rises close to the highest level ever upriver in Memphis. (Photo by Mario Tama/Getty Images)

Salar de Uyuni (or Salar de Tunupa) is the world's largest salt flat at 10,582 square kilometers (4,086 sq mi). It is located in the Potosí and Oruro departments in southwest Bolivia, near the crest of the Andes, and is elevated 3,656 meters (11,995 ft) above mean sea level. The Salar was formed as a result of transformations between several prehistoric lakes. It is covered by a few meters of salt crust, which has an extraordinary flatness with the average altitude variations within one meter over the entire area of the Salar.

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.

Vivid colors and bizarre shapes come together in a false-color image that could be an illustration for a fantasy story. This labyrinth of exotic features winds its way along the edge of Russia’s Chaunskaya Bay in northeastern Siberia, seen as a vivid blue half-circle at the bottom of the image Two major rivers, the Chaun and Palyavaam, flow into the bay, which in turn opens into the Arctic Ocean. Ribbon lakes and bogs are present throughout the area, created by depressions left by receding glaciers. (Photo by USGS/NASA)

Alex Prager is an American art photographer and filmmaker based in Los Angeles. Her photographs primarily use staged actors, models and extras to create “meticulously designed mise en scène”, often described as film-like and hyperreal. “Alex Prager: Silver Lake Drive” is at the Photographers’ Gallery, London, 15 June – 14 October 2018. Here: The Big Valley, Susie and Friends, 2008. (Photo by Alex Prager Studio/Lehmann Maupin Gallery)