Namtso or Lake Nam (officially: Nam Co; Mongolian: Tengri Nor; “Heavenly Lake”; 30°42′N 90°33′E / 30.7°N 90.55°E / 30.7; 90.55) is a mountain lake on the border between Damxung County of Lhasa Prefecture and Baingoin County of Nagqu Prefecture in the Tibet Autonomous Region of China, approximately 112 kilometres (70 mi) NNW of Lhasa.