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)

Though schools around the globe have different start dates, calendars and traditions, the first day of a new term is an exciting time filled with the prospects of gaining more knowledge, making new friends and building community. Here: Schoolchildren attend their first lesson on Knowledge Day in the town of Turov, Zhytkavichy District, Gomel Region, Belarus on September 1, 2017. Knowledge Day marks the beginning of a new school year in Belarus and is celebrated on September 1. (Photo by Viktor Drachev/TASS via Getty Images)

Elderly women wait for customers as they sell their self-made food products at a street market, with a graffiti depicting Russian President Vladimir Putin on the wall of a house seen in the background, in the town of Kashira, outside Moscow, Russia on October 10, 2017. (Photo by Andrey Volkov/Reuters)

A horse buggy is headed for the stables on a foggy night in New Orleans, Monday, December 18, 2017. (Photo by David Grunfeld/NOLA.com The Times-Picayune via AP Photo)

Eddie Ladd and Gwyn Emberton perform as Dylan and Caitlin Thomas in “Caitlin” at the Lauriston Hall, Edinburgh, Scotland on August 25 2017. (Photo by Mary Turner/Reuters)

An injured person is seen after an earthquake hit Port-au-Prince, Haiti, Tuesday, January 12, 2010. A 7.0-magnitude earthquake, the largest ever recorded in the area, rocked Haiti on Tuesday. (Photo by Jorge Cruz/AP Photo)

The buildings of the banking district are seen through thousands of rain drops on a glass railing in central Frankfurt, Germany, Wednesday, January 11, 2017. (Photo by Michael Probst/AP Photo)

In this Sunday, May 29, 2016 photo, fighters take a selfie while firing artillery during fight against Islamic State militants in Fallujah, Iraq. Iraqi forces this week pushed into the city's southern sections after securing surrounding towns and villages more than 50,000 people are believed to be trapped inside the Sunni majority city, about 65 kilometers (40 miles) west of Baghdad. (Photo by Anmar Khalil/AP Photo)