A giant river otter, the world's largest otter species, looks out of its enclosure at the newly completed River Safari in Singapore, on March 25, 2013. (Photo by Wong Maye-E/Associated Press)

These photographs of hundreds of ducks following their leader down a river are truly mesmerizing. Rafeur Rahman of Bangladesh climbed a high bridge and saw hundreds of ducks apparently playing a game of follow the leader. More than 500 ducks live on the river, where the mosses and snails provide the perfect habitat. Here: Ducks in the river Baral in Bangladesh. (Photo by Rafeur Rahman/Caters News Agency)

A Hindu holy man or Sadhu walks back to his ashram after taking a dip at Sangam, confluence of Ganges river, Yamuna river and mythical Saraswati river in Allahabad, India, Thursday, August 4, 2016. (Photo by Rajesh Kumar Singh/AP Photo)

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)

A Hindu devotee drinks water from the Ganges River at the Sangam area, the confluence of rivers Ganges, Yamuna, and the mythical Saraswati, in Allahabad on March 16, 2021. (Photo by Sanjay Kanojia/AFP Photo)

Men rest on a boat in the overflowed Ganges River under the Shastri Bridge in Allahabad on August 17, 2022, as water levels of the Ganges and Yamuna rivers rose following monsoon rainfalls. (Photo by Sanjay Kanojia/AFP Photo)

A dead red-tailed monkey hangs by its tail above the ground, in order to keep it away from ants, in the forest near the city of Mbandaka, Democratic Republic of the Congo, April 5, 2019. Bushmeat hunters are emptying Central Africa's forests at a high rate, researchers say. A growing appetite for wild meat in cities has ramped up the scale of hunting. Research shows around 6 million tonnes of bushmeat are sourced annually from the Congo Basin, whose forest spans across six countries and is second in size only to the Amazon. (Photo by Thomas Nicolon/Reuters)

A Colombian Nukak Maku Indian boy gestures in a refugee camp at Agua Bonita near San Jose del Guaviare of Guaviare province September 3, 2015. Since emerging from the jungle in 2005, half naked and carrying blowpipes, the Nukak have lived in settlements near the frontier town of San Jose del Guaviare, a humid outpost in the Amazon 400 km (250 miles) southeast of the capital Bogota. (Photo by John Vizcaino/Reuters)