The Mekong River has become a new front in the U.S.-China rivalry, environmentalists and officials say, with Beijing overtaking Washington in both spending and influence over downstream countries at the mercy of its control of the river's waters.

It's a confrontation in which the administration of U.S. President Donald Trump — which has largely maintained funding for Barack Obama-era environmental and development programs in the Lower Mekong — is losing ground.

The two powers' struggle recently moved into the realm of science — with the U.S. and Chinese governments each touting different reports about whether China's 11 dams on the river were harming nations downstream.