In this January 12, 2015 photo, a wall of collectable sneakers are displayed at Sneaker Pawn in the Harlem section of New York. Basketball sneakers can re-sell for hundreds of dollars, depending on the model, the size of the production run and how easy it is to find a pair in good condition. (Photo by Seth Wenig/AP Photo)

In this March 14, 2015 photo, tourists take pictures from a viewing area at Iguazu Falls in Brazil. From walkways and bridges, viewers can count 270 water falls almost 100 meters (330 feet) high. (Photo by Jorge Saenz/AP Photo)

Students in Aone’s elementary school during break in between the class on April 9, 2015. The school has only six students, two of whom are from the same family. Similarly small schools can be found throughout Japan. (Photo by Ko Sasaki/The Washington Post)

In this photo taken on February 21, 2017, shooting instructor Kim Su- Ryon poses for a portrait at the Meari Shooting Range in Pyongyang Kim is holding a “Paektusan” target pistol, gifted by late North Korean leader Kim Il- Sung. Visitors to the range can pay 10 USD to shoot ten rounds. (Photo by Ed Jones/AFP Photo)

A woman is cooled down with a watering can as she sunbathes using insulating tape, at a beauty center in Belo Horizonte, Brazil, on December 21, 2017. Brazilian women take advantage of the beginning of the summer to sunbathe using the new national trend: natural tanning with insulating tape. Instead of using tiny bikinis on the beach, women avoid being bothered or stalked by getting taped in the shape of them, and lay in the sun over rooftops to enjoy the morning sun and get the perfect “marquinha” tan lines. (Photo by Douglas Magno/AFP Photo)

Iraqi teenagers swim in waste water from the nearby Tuweitha nuclear facility near Baghdad, Iraq on May 28, 2003. Iraqis are consuming contaminated water unaware of the dangerous pollutants that can cause severe ill health. (Photo by Damir Sagolj/Reuters)

An Indian rag picker collects plastic bags at an industrial area on the outskirts of Jammu, India, Tuesday, June 5, 2018. The U.N. says government bans on plastic can be effective in cutting back on waste but poor planning and follow-through have left many such bans ineffective. (Photo by Channi Anand/AP Photo)

National Geographic photographer Steve Winter has spent most of his adult life shooting wild cats. Photo: A 14-month-old cub, cooling off in a pond, is riveted by a deer that appeared near the shore. Tigers are powerful swimmers; they can easily cross rivers four to five miles wide and have been known to swim distances of up to 18 miles. (Photo by Steve Winter/National Geographic)