These two young siblings appear to cling on to a tree for dear life and even hold hands as they learn the ropes of climbing, on June 25, 2013. (Photo by Tim Fitzharris/Minden/Solent)

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)

Cattle keepers from the Dinka tribe perform a traditional dance after a prayer session for peace and good health along the route to Rajaf Payam outside the capital Juba October 18, 2014. (Photo by Jok Solomon/Reuters)

An actress dressed as Wonder Woman walks between visitors during the season inauguration of the Madrid Warner amusement park in San Martin de Valdeiglesias, near Madrid, Spain, March 18, 2016. (Photo by Andrea Comas/Reuters)

A person dressed as cartoon character Homer Simpson sits on an NYPD security barricade in Times Square as preparations are made for New Years Eve in New York December 29, 2014. (Photo by Carlo Allegri/Reuters)

People look at a loaded truck that got stuck in a sinkhole on a road in Guilin, Guangxi Zhuang Autonomous Region, January 7, 2015. No injury was reported, according to local media. (Photo by Reuters/Stringer)

Members of ASC Tornados, the motorcycle display team of the Indian army, lie in a row on the ground as another performs a stunt by jumping over them during the 225th anniversary celebrations of Army Service Corps in Bangalore, India, Tuesday, December 8, 2015. The Army Service Corps which was established in 1790 is an arm of the Indian Army which handles its logistic support function. (Photo by Aijaz Rahi/AP Photo)

A demonstrator is detained by police officers during clashes in downtown Barcelona, Spain, Friday, October 30, 2020. Clashes have erupted in a central Barcelona square between anti-riot police and hundreds who had gathered to protest the mandatory closure of bars, restaurants and other businesses in the latest effort to rein in on coronavirus outbreaks. (Photo by Joan Mateu/AP Photo)