Phnom Penh, CambodiaThere was a time when scores of some of the world’s largest freshwater fishes swam up the Mekong River, past the Laotian town of Luang Prabang, now a UNESCO World Heritage site.

Giant catfish the size of grizzly bears, seven-striped barb, giant pangasius, and other huge fish once made their way past the city’s historic Buddhist temples, French colonial villas, and traditional wooden buildings on their way north to their spawning grounds. Following decades of overfishing in the Mekong River, it’s a rarity to see such river titans today. (Read how the giant freshwater stingray is likely the world’s biggest freshwater fish.)

Still, many scientists held out hope for their recovery: As long as the Mekong