Riot security forces clash with demonstrators as a motorcycle is set on fire during a protest against Venezuelan President Nicolas Maduro's government in San Cristobal, Venezuela May 29, 2017. (Photo by Carlos Eduardo Ramirez/Reuters)

Growing cities, overuse of fertilizers and factory wastewater have degraded China's water supplies to the extent that half the nation's rivers and lakes are severely polluted. China aims to spend $850 billion to improve filthy water supplies over the next decade, but even such huge outlays may do little to reverse damage caused by decades of pollution and overuse in Beijing's push for rapid economic growth. Photo: Fishermen row a boat in the algae-filled Chaohu Lake in Hefei, Anhui province, June 19, 2009. (Photo by Jianan Yu/Reuters)

Internationally acclaimed German three-dimensional artist Manfred Stader adds finishing touches to his artwork in Cape Town, South Africa on 21 November 2010. Stader created this masterpiece to celebrate the opening of Speedo's first dedicated concept store in Africa. (Photo by Foto24/Gallo Images/Getty Images)

A 19th century bicycle safety lock is displayed in an old frame in the Museum of Domenico Agostinelli in Dragona, near Rome October 30, 2014Italian collector Domenico Agostinelli, 74, has a passion that has led him over the past 60 years to pick up and collect things of all types, from antique art to everyday objects of the past and present. His collection includes a 65-million-year-old dinosaur egg, meteor fragments, a car that once belonged to American mob boss Al Capone, a lock of hair of Italian national hero Giuseppe Garibaldi, toys, weapons, musical instruments of all kinds and many more. (Photo by Tony Gentile/Reuters)

A boy jumps from a swing during sunset in Valras-Plage, southern France December 29, 2014. (Photo by Yves Herman/Reuters)

A woman waters the plants outside her house in an alley at a slum in Mumbai October 28, 2014. (Photo by Danish Siddiqui/Reuters)

Konishiki “The Dumptruck” of Hawaii stares down at his opponent during the first Sumo Bashai held outside Japan, at the Albert Hall in London, England. (Photo by Chris Cole /Getty Images). 1991

The possible surface of TRAPPIST-1f, one of seven newly discovered planets in the TRAPPIST-1 system that scientists using the Spitzer Space Telescope and ground based telescopes have discovered. (Photo by Reuters/NASA/JPL-Caltech)