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)

Residents wade through flood waters from Tropical Storm Harvey in Beaumont Place, Houston, Texas on August 28, 2017. Houston was still largely paralyzed Monday, and there was no relief in sight from the storm that spun into Texas as a Category 4 hurricane, then parked itself over the Gulf Coast. (Photo by Jonathan Bachman/Reuters)

A women sell food under the wing of a plane wreckage being used as housing in M'Poko Internally Displaced Persons camp in Bangui, Central African Republic on Saturday, February 13, 2016. The M'Poko IDP camp, just outside the capitol's airport, currently houses close to 20,000 people displaced due to the ongoing conflict in Central African Republic. (Photo by Jane Hahn/The Washington Post)

A Syrian refugee girl covers herself with a blanket as she stands outside tents at a makeshift settlement in Bar Elias in the Bekaa valley January 5, 2015. Lebanon enforced new immigration controls at the Syrian border on Monday in a move to gain control of the steady stream of refugees from its much larger neighbour. (Photo by Mohamed Azakir/Reuters)

Church members pray at the Dolieb Hill Presbyterian Church in the Protection of Civilians (POC) site at the United Nations Mission in South Sudan (UNMISS) compound in Malakal, South Sudan on Saturday, July 9, 2016. (Photo by Jane Hahn/The Washington Post)

In this January 4, 2016 photo, the weapon of a rebel fighter for the 36th Front of the Revolutionary Armed Forces of Colombia, or FARC, hangs from a branch serving as a makeshift clothesline, near a rebel camp, in Antioquia state, in the northwest Andes of Colombia. “We’ll lay aside our weapons, like the accord says, but never hand them over”, says Juan Pablo, a commander of the 36th Front. (Photo by Rodrigo Abd/AP Photo)

Arisha, 9, takes instructions from coach Younus Qambrani during an exercise session at the first women's boxing coaching camp in Karachi, Pakistan February 19, 2016. For the past six months about a dozen girls, aged 8 to 17, have gone to the Pak Shine Boxing Club after school to practice their jabs, hooks and upper cuts. (Photo by Akhtar Soomro/Reuters)