A dog swims as a resident navigates his boat in a neighbourhood flooded by the Purus river, which continues to rise from days of heavy rainfall in the region, in Boca do Acre, Amazonas state March 14, 2015. According the state civil defense, more than 20,000 people have been left homeless along the Purus river, where incessant rains have flooded the area and caused the river to burst their banks. (Photo by Bruno Kelly/Reuters)

A Christian pilgrim is baptised by a priest in the muddy water of the Jordan River at the Kasser-Al-Yahud baptismal site near the West Bank city of Jericho, on April 11, 2017. According to the gospels Jesus Christ was baptised in the waters of the Jordan River by John the Baptist. (Photo by Gali Tibbon/AFP Photo)

Local people check the growth of mussels at a river in Haian County on November 2, 2017 in Nantong, Jiangsu Province of China. Fish, shrimp, crab and mussel farming cleans the river and increases the villagers' income at Haian county in Jiangsu. (Photo by VCG/VCG via Getty Images)

A boat commutes across the Mekong river in Phnom Penh on August 8, 2014. The Mekong is the world's twelth longest river running from the Tibetan Plateau through China's Yunnan province, Myanmar, Laos, Thailand, Cambodia and Vietnam. (Photo by Tang Chhin Sothy/AFP Photo)

Policemen and residents run as waves from a tidal bore surge past a barrier on the banks of Qiantang River in Haining, Zhejiang province August 31, 2011. As Typhoon Nanmadol approaches eastern China, the tides and waves in Qiantang River recorded its highest level in 10 years, local media reported. (Photo by Reuters/China Daily)

The Rio Tinto river in Spain crosses an ancient mining site which makes the water turn a variety of bright colours. Copper, silver and gold are mined here, as well as iron, which turns the water red. An ochre mix is responsible for the yellow tint of the rest of the river. (Photo by Olivier Jarry-Lancombe/Solent News)

A monkey drinks water from a tap on a hot afternoon in Jammu, the winter capital Kashmir, India, 17 May 2016. Temperatures of around 42 degrees Celsius were forecast in the region. According to the news reports the Indian government decided to divert water by its river interlinking plans from rivers like Brahmaputra and the Ganges towards those rivers facing the drought likesituation . Many Indian states have been affected by drought and have been hit hard by water scarcity. (Photo by Jaipal Singh/EPA)

“Winter shapes, Moscow river”. Moscow river at this part is never covered by ice. When the temperature is very low it's possible to see a strong fog. Morning light and pipes of the oli factory creates a fantastic landscape. Photo location: Moscow, Russia. (Photo and caption by Sergey Rumyantsev/National Geographic Photo Contest)