New megadams threaten world’s biggest fish

Many endangered fish, such as the Mekong giant catfish, will suffer amid a new push to build dams in Laos and other tropical regions, experts say.

A fisherman navigates extremely low water levels on the Mekong River in northeastern Thailand in 2019. A dam upstream in Laos, as well as drought, caused the reduced flow.

There 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 River south of China remained undammed, smaller scale fishing and other conservation efforts could eventually lead to the recovery of these critically endangered species.

But now that hope appears to be dimming, with Laos planning to construct at least 10 new dams on the Mekong’s main stem in the next decade. Among the first projects is Nam Sang, a massive hydropower plant to be constructed just upstream of Luang Prabang. 

Laos’ Communist regime, which promotes hydropower as part of its bid to become the battery of Southeast Asia, has built dozens of dams on Mekong tributaries. The government hopes new dams, such as Nam Sang—to be completed by 2027—will generate government revenue by selling electricity to neighboring countries, such as Thailand.

“If these dam projects go ahead, the stretch of the Mekong that was...

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