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)

Lake Baikal is the world's oldest lake, at 25 million years (possibly older), and deepest, averaging 744.4 metres (2,442 ft).

Located in the south of the Russian region of Siberia, between Irkutsk Oblast to the northwest and the Buryat Republic to the southeast, it is the most voluminous freshwater lake in the world, containing roughly 20% of the world's unfrozen surface fresh water.

In this photo taken Wednesday, October 29, 2014, a fisherman catches a fish near the shores of Lake Chivero, west of Harare. Illegal fishing can be hazardous in Zimbabwe, where poachers scan the banks for armed rangers and the water for crocodiles while they cast their rods. The country is in such a dire economic state that thousands of people, unable to find regular work, flock to Lake Chivero in hopes of catching fish, mostly bream, that they can sell for desperately needed income. (Photo by Tsvangirayi Mukwazhi/AP Photo)

An Andean man and a woman, depicting Inca's legendary characters Manco Capac and Mama Ocllo, pose for a portrait in a Uros island at Lake Titicaca before a re-enactment in Puno November 5, 2014. The Uros islands are a group of 70 man-made totora reed islands floating on the lake, which according to Peru's tourism board iPeru is the world's highest navigable lake at over 4,000 meters above sea level. The Uros people fish and hunt, but tourism is their main source of livelihood. (Photo by Enrique Castro-Mendivil/Reuters)

Migingo is a tiny 2,000-square-metre (0.49-acre; 0.20-hectare) island, about half the size of a football pitch, in Lake Victoria. Migingo is a tiny rock island, less than half-an-acre or about half the size of a football field, located in Lake Victoria, the largest lake in Africa and the largest tropical lake in the world. Although tiny in size, the island is home to 131 people (according to 2009 census) living in crammed huts made of corrugated sheets and wood. Despite shabby living conditions, Migingo Island boasts of five bars, a beauty salon, a pharmacy as well as several hotels and numerous brothels.

The Lake of Lights at Talkin Tarn lake near Brampton in Cumbria, England on October 22, 2017 – where hundreds of lights in the surrounding woodland represent a cherished memory of a relative friend or loved one no longer with us. (Photo by Owen Humphreys/PA Images via Getty Images)

A cyclist rides the path around Lake Harriet on Memorial Day in Minneapolis on Monday, May 25, 2020. The area around the Lake Harriet Bandshell was busy but not crowded on Memorial Day evening. (Photo by Jeff Wheeler/Star Tribune via AP Photo)