With about 10 more dams planned for the mainstream Mekong’s lower reaches and hundreds more on its tributaries, a lifeline for 60 million people is being choked. Tens of millions more will be affected as farms and fisheries are compromised, even as the rich and powerful across the region profit from the hydropower business.

“We’re asking the question: Is this the breaking point for the Mekong?” said Brian Eyler, the director of the Stimson Center’s Southeast Asia program and the author of “Last Days of the Mighty Mekong.” “The Mekong’s ecosystem is adaptable and resilient but the worry is that the river’s massive resource base won’t be able to overcome all these dams and extreme weather.”

The Mekong has been so exhausted that the Thai government, long lackadaisical about environmental protection, announced on Feb. 5 that it had rejected long-held Chinese ambitions to blast rocks in the river to allow for bigger boats and more trade. Environmental groups warned that further manipulation of the river could be catastrophic.

Ever since China, where the headwaters of the Mekong are fed by glacial melt, began damming the river early this century, the river has been producing less fish. For a population downstream that could once count on the world’s most abundant inland fishery for much of its protein intake, this change has been devastating.

Amkha Janlong, 69, remembers how, not that long ago, she would go to a pier in Nong Khai and watch men heave in catches of fish taller and heavier than they were. The biggest of all, the Mekong giant catfish, weighs more than a tiger and used to feed entire villages.