Climate change disrupts ancient rhythms of mekong river, threatening over 1,000 fish species

The mighty Mekong River, flowing through Southeast Asia, supports one of Earth’s most spectacular freshwater ecosystems with more than 1,000 fish species. Among its inhabitants are giants like the critically endangered Mekong giant catfish and giant barb, both now facing an unprecedented threat as climate change fundamentally alters the river’s natural patterns.

For millennia, these fish have synchronized their lives with the Mekong’s predictable annual flood pulse, triggered by seasonal monsoons. This flooding expands their habitat and signals spawning time for species that migrate vast distances along the river system. But climate change is throwing this ancient rhythm into chaos, making monsoon seasons increasingly unpredictable and erratic.

The consequences are already visible in Cambodia’s Tonle Sap Lake, the region’s crucial fish nursery. In recent years, weak monsoons have prevented the lake from expanding to its historical size, dramatically shrinking available habitat for migratory fish. Local fishing communities, whose floating villages rise and fall with the water levels, immediately feel the impact through reduced catches and disrupted livelihoods.

“Climate change is a great unknown,” warns Zeb Hogan, a biologist at the University of Nevada, Reno, highlighting how this new threat compounds existing pressures. The Mekong’s fish already face challenges from dam construction, pollution, and overfishing. Now, with climate change adding another layer of instability, scientists are racing to understand how these combined stressors might push the world’s most biodiverse river system toward ecological collapse.