With its source in the Yunnan mountains in China, the Black River (Song Da) carves out a deep canyon through the northwest corner of Vietnam, a region dominated by peaks higher than 2 000m. At Muong Lay, its gorges cross those of the Nam Na. A dam inaugurated in 2016 flooded the valley downstream of Muong Te. In this region, which does not see many tourists, there are people from Vietnam's five linguistic families.