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.

A house along Hoover Beach is covered by ice from high winds and from the waves from Lake Erie, Saturday, February 29, 2020, in Hamburg N.Y. Blowing snow has fallen around the state since Thursday, though the heaviest snowfall was concentrated in largely rural areas east of Lake Erie and Lake Ontario. (Photo by Jeffrey T. Barnes/AP Photo)

In this aerial view fishing boats are seen on the shore of the Lake Malawi at the Senga village on May 20, 2019 in Senga, Malawi. Hundreds of local traders gather each morning and afternoon at Senga, but fish populations are falling in Lake Malawi, Africa's third largest body of freshwater. (Photo by Gianluigi Guercia/AFP Photo)

Czech fishermen sort fish during the traditional Carp haul at Lake of Dvoriste near Smrzov village, Czech Republic, 02 November 2015. Carp, the traditional Czech Christmas Eve dinner, is harvested primarly from the region of southern Bohemian lakes. (Photo by Filip Singer/EPA)

A worker lays rails across the bed of a drained area of a lake used for the production of salt at the Sasyk-Sivash lake near the city of Yevpatoria in Crimea, October 5, 2014. The area has a long tradition of salt production, prepared from salt flats flooded with water from the Black Sea. (Photo by Pavel Rebrov/Reuters)

A swimmer disguised as Superman dives into the lake during the 78th “Coupe de Noel” (Christmas cup) swimming race in the Lake Geneva, on December 18, 2016 in Geneva. More than 1800 participants took part in the event, a 12-meter-long swimming off the Geneva's bank in the 7 degrees Celsius cold water. (Photo by Fabrice Coffrini/AFP Photo)

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.