China has long wanted to dredge the riverbed in northern Thailand to open passage for massive cargo ships — and potentially military vessels.

Ultimately a link could be carved from Yunnan province thousands of kilometers south through the Mekong countries — Myanmar, Laos, Thailand, Cambodia and Vietnam.

There, the river emerges into the South China Sea, one of the world’s busiest shipping lanes and the centerpiece of Beijing’s trade and security strategy for its Asian neighborhood.

Under the tagline “Shared River, Shared Future” China insists it seeks only the sustainable development of the river and to split the spoils of a trade and energy boom with its Mekong neighbors and their market of 240 million people.

But squeezed for value by the dams lacing China’s portion of the river — and further downstream — the Mekong is already changing.

Fish stocks have collapsed say Thai fisherman, and nutrient-rich land in the Vietnamese delta is sinking as the sediment flow shrinks.

The river is rivaled only by the Amazon for its biodiversity, environmentalists say, but now endemic species like the giant Mekong catfish and river dolphins are facing extinction.

Environment versus big business. Geopolitics throttling a lifeline to 60 million people — big themes are playing out on a slow-moving river.