Bangladeshi railway police try to clear line, as thousands of Bangladeshi Muslims gather to board trains to return home after attending three-day Islamic Congregation on the banks of the River Turag in Tongi, 20 kilometers (13 miles) north of the capital Dhaka, Bangladesh, Sunday, January 26, 2014. (Photo by A. M. Ahad/AP Photo)

A general view of dried-up rivers in the Pilbara region of Western Australia December 2, 2013. Western Australia's Pilbara region, which is the size of Spain, has the world's largest known deposits of iron ore and supplies nearly 45 percent of global trade in the mineral. (Photo by David Gray/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)

“Hydrocynus goliath, also known as the goliath tigerfish, giant tigerfish or mbenga, is a very large African predatory freshwater fish. The giant tigerfish is restricted to the Zaire River system, Lualaba River, Lake Upemba and Lake Tanganyika”. (Photo by Tigerfishcamp / Tourettefishing / Bigfishesoftheworld)

An onlooker watches as the “Disney Fantasy” cruise ship is hauled backwards by a tugboat down the Ems River after the ship departed from the Meyer Werft shipyards on January 20, 2012 in Papenburg, Germany. The completed 130,000-tonne ship, which is 1,115 feet long and can accomodate 5,450 passengers, cast and crew, was on its way to the North Sea. (Photo by Sean Gallup/Getty Images)

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)

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)