A man (2nd L) takes pictures as visitors run away from a wave caused by a tidal bore which surged past a barrier on the banks of Qiantang River, in Hangzhou, Zhejiang province August 14, 2014. (Photo by Reuters/Stringer)

Jan Kara (R) and Jan Holan pedal their boat, made with plastic bottles, on the Elbe river near Kostelec nad Labem July 15, 2014. Jan Kara, a 22-year-old student, and Jakub Bures, a 22-year-old car mechanic, built the 10-metre (32.8-feet) long boat from 5000 plastic bottles strapped to a wooden frame. (Photo by David W. Cerny/Reuters)

Widows, who have been abandoned by their families, light sparklers after offering prayers on the banks of the river Yamuna as part of Diwali celebrations organised by non-governmental organisation Sulabh International in Vrindavan, Uttar Pradesh October 21, 2014. (Photo by Ahmad Masood/Reuters)

A devotee offers prayers to the setting sun during the "Chhat" festival at Bagmati river in Kathmandu, Nepal November 17, 2015. Hindus in Nepal celebrate "Chhat", a four-day festival that honours the sun god, by praying at sunrise and sunset, and seek blessings for one's family by giving offerings. (Photo by Navesh Chitrakar/Reuters)

Long-tailed mayflies (Palingenia longicauda) at Tisza river near Tiszainoka 135km (84 miles) southeast of Budapest, June 23, 2013. 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)

National Geographic photographer Steve Winter has spent most of his adult life shooting wild cats. Photo: A 14-month-old cub, cooling off in a pond, is riveted by a deer that appeared near the shore. Tigers are powerful swimmers; they can easily cross rivers four to five miles wide and have been known to swim distances of up to 18 miles. (Photo by Steve Winter/National Geographic)

Hungarian pilot and European champion Zoltan Veres flies under the oldest Hungarian bridge, the “Lanchid” (Chain Bridge) with his “MXS” type plane on May 1, 2014 during a Red Bull flying and car show around the Danube River of Budapest downtown. (Photo by Attila Kisbenedek/AFP Photo)

View of a damaged bridge at the Iguacu Falls on June 12, 2014, in Foz do Iguacu, Brazil, following the overflowing of the Parana river. In neighbouring Paraguay flooding has forced the evacuation of about 150,000 people in Paraguay's capital city Asuncion, authorities said. (Photo by Norberto Duarte/AFP Photo)