Now, in an energy-hungry age on the continent, the rivers share another distinction, as wellsprings of financial temptation for the struggling countries that rely on their flow, Laos and Myanmar (Burma). Both countries are grappling with decisions on whether to build massive hydropower dams on the two significant rivers. The projects could put fragile ecology and associated livelihoods at risk, but the dams could help the two countries reap billions of dollars by exporting the megawatts to China and Thailand, two neighbors with rapidly growing energy demand.

For now, it looks like the two nations are taking different paths. In Laos, the government appears to be going ahead with the $3.8 billion Xayaburi dam on the Mekong River-despite opposition by environmental