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