The Mekong is the world's eighth longest river, flowing through China, Myanmar, Laos, Cambodia, Thailand and Vietnam. For centuries, it's been a source of cooperation. But it's also subject to contention, especially in recent decades when China began building hydropower stations on its upper reaches. The controversy boiled up again recently, after a study funded by the U.S. State Department accused China of having held back large amount of water in its reservoirs, exacerbating a severe drought in Southeast Asia last year. Our cameras have been granted exclusive access to some of the hydropower stations on the river.