A young boy uses a rope to drag himself across the raging Sahong channel at Khone Falls in Laos.

The Sahong channel is the only channel in the area without a waterfall—and is the proposed site for a hydroelectric dam that environmentalists say will cut off a vital migratory fish route.

So far the Mekong remains almost untouched. Only China has dammed the main stream of the river at two locations. But there are now plans for a dozen dams to be built on the Mekong in China, Laos, and Thailand.

"The Mekong River is the most productive river on Earth," said Hogan of the Megafishes Project.

"The damming of the river could have devastating consequences for fisheries."

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