Boat crew members train on the waters of the Tonle Sap River on the morning of the first day of the Water Festival on November 13, 2016 in Phnom Penh, Cambodia. The yearly three-day Water Festival is one of the most important holidays in Cambodia and celebrates the end of the rainy season and the start of the rice harvesting. The Festival also coincides with the Tonle Sap river reversing course, which it does twice a year. Approximately 2 million people are expected to attend this year's festival, during which 259 boats and nearly 20,000 oarsmen will participate in the races. After a fatal stampede resulting in the death of some 353 people during the Water Festival in 2010, it has been cancelled four times over the past five years, with weather used as an official excuse. (Photo by Omar Havana/Getty Images)

South Korean divers prepare to plunge through a hole in the ice of the frozen Imjin River on January 16, 2005 in Yeonchun, South Korea. (Photo by Chung Sung-Jun/Getty Images)

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)

The London Eye is a giant Ferris wheel on the South Bank of the River Thames in London. Also known as the Millennium Wheel, its official name was originally the British Airways London Eye, then the Merlin Entertainments London Eye, and since January 2011, the EDF Energy London Eye.

Hamar women dance before a bull jumping ceremony in Ethiopia's southern Omo Valley region near Turmi on September 19, 2016. The Hamar are a Nilotic ethnic group in Ethiopia. The construction of the Gibe III dam, the third largest hydroelectric plant in Africa, and large areas of very “thirsty” cotton and sugar plantations and factories along the Omo river are impacting heavily on the lives of tribes living in the Omo Valley who depend on the river for their survival and way of life. (Photo by Carl De Souza/AFP Photo)

A Nepalese Hindu devotee bathes in the Bagmati River on her way to the Pashupatinath Temple to offer prayers to Lord Shiva, Hindu god of destruction during Shravan festivities in Sundarijal, on the outskirts of Kathmandu on August 3, 2015. According to the Nepali calendar, Shravan is considered the holiest month of the year with each Monday of the month known as Shravan Somvar when worshippers offer prayers for a happy and prosperous life. (Photo by Prakash Mathema/AFP Photo)

Rowers enter in Canaregio river during the 42nd Venice Vogalonga on May 15, 2016 in Venice, Italy. 42 years ago a group of Venetians, both amateur and professional rowers, came up with an idea of non-competitive race in which any kind of rowing boat can take part. The first Vogalonga began with the message to protest against the growing use of powerboats in Venice and the swell damage they do to the historic city. (Photo by Awakening/Getty Images)

Long-tailed mayflies (Palingenia longicauda) mate on the surface of the Tisza river near Tiszakurt, Hungary, June 14, 2016. Millions of these short-lived mayflies engage in a frantic rush to mate and reproduce before they perish in just a few hours during “Tiszaviragzas” or Tisza blooming season from late spring to early summer every year. (Photo by Laszlo Balogh/Reuters)