A security exercise takes place along the River Thames on January 19, 2012 in London, England. The exercise including around 44 police officers, 94 military personnel, 15 boats and a Royal Navy Lynx helicopter was conducted by both the Metropolitan Police and the Royal Marines and designed to test their joint capability ahead of the 2012 London Olympic Games. (Photo by Dan Kitwood/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)

Ethnic Cham Muslim people pass the time near their boats on banks of Mekong river in Phnom Penh July 29, 2013. About 100 ethnic Cham families, made up of nomads and fishermen without houses or land who arrived at the Cambodian capital in search of better lives, live on their small boats on a peninsula where the Mekong and Tonle Sap rivers meet, just opposite the city's centre. The community has been forced to move several times from their locations in Phnom Penh as the land becomes more valuable. They fear that their current home, just behind a new luxurious hotel under construction at the Chroy Changva district is only temporary and that they would have to move again soon. (Photo by Damir Sagolj/Reuters)

Floating on clear deep water and reflections near the cave entrance. Visitors can either bring their own kayaks or rent boats from the local community to paddle deep inside the cave and marvel at its wonders on March 2015 at Tham Khoun Ex, Laos. Tham Khoun Xe, commonly known as the Xe Bang Fai River Cave, in Laos, has over 15km of passages filled with awe-inspiring views and wide expanses of water. Photographer, John Spies, 59, captured scenes from the entrances of the huge underground river passages, intricate cave formations and views from a passage high above the water. The cave is formed by the Xe Bang Fai river, a major tributary of the Mekong and in the dry season can be traversed using inflatable kayaks. (Photo by John Spies/Barcroft Media/ABACAPress)

Incredible drone image capture colourful water lilies being harvested in An Giang Province, Vietnam, Southeast Asia on September 2020. Water lilies are an iconic symbol in the Mekong Delta and the flowers are immediately sent to market before landing on meal tables. Their stalks are edible and can be eaten raw with either fermented paste or braised sauce, or dunked into sour soup or hotpot. (Photo by Nguyen Sanh Quoc Huy/Triangle News)

Iguazu Falls are waterfalls of the Iguazu River on the border of the Brazilian state of Paraná and the Argentinian province of Misiones. The falls divide the river into the upper and lower Iguazu. The Iguazu River rises near the city of Curitiba. It flows through Brazil for most of its course. Below its confluence with the San Antonio River, the Iguazu River forms the boundary between Argentina and Brazil.

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)

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)