Among the fish populations that could be harmed by the Xayaburi dam in Laos is the critically endangered Mekong giant catfish, considered by the Guinness Book of World Records to be the world’s largest freshwater fish. The fish, which grows to 650 pounds and about 10 feet long, is only found in the Mekong River. It is migratory, moving between downstream habitats in Cambodia upstream to northern Thailand and Laos each year to spawn. Some experts fear the Xayaburi dam could block the migration and drive the giant catfish to extinction. (Photo by Courtesy of Zeb Hogan/University of Nevada, Reno)

Two stallions confront each other at a horse fighting contest in Rongshui, China. More than 30 horses from surrounding regions took part in the traditional activity of the Lantern festival. (Photo by China Foto Press)

Georgian men take a break from selling fruit and vegetable at a street market in Tbilisi, Georgia, Wednesday, July 20, 2016. (Photo by Shakh Aivazov/AP Photo)

A competition, now in its 43rd year, dedicated to showcasing the beautiful and bizarre as seen under a light microscope attracted over 2,000 entries from 88 countries. Here: Honorable Mention by Emre Can Alagöz, Istanbul, Turkey: The eyes of a jumping spider, magnified 6x. (Photo by Emre Can Alagöz/2017 Nikon Small World Photomicrography Competition)

Parade participants during the traditional “Masopust Carnival” festival on February 13, 2018 in Roztoky near Prague, Czech Republic. Known as Masopust (literally, “giving up meat”), the festival was traditionally the last chance to eat and drink in excess before the austerity of Lent. (Photo by Margot Buff/RFE/RL)

Rohingya refugee sisters Nur Kaida (R) and Ruhana hug each other at their shelter at the Palongkhali refugee camp near Cox's Bazar, Bangladesh December 21, 2017. (Photo by Marko Djurica/Reuters)

Prince Philip, the Duke of Edinburgh meets members of the cast of “Chicago” during a visit to the Adelphi Theatre in this March 4, 1999 file photo in London, England. (Photo by Anwar Hussein/Getty Images)

A cat sits in the flooding waters from Hurricane Matthew in downtown Nichols, South Carolina, October 10, 2016. (Photo by Randall Hill/Reuters)