諒山省
The Bắc Khê () is a left tributary of the Kỳ Cùng River. It is 54 km long with a catchment area of 801 km2 and flows through Tràng Định District in Lạng Sơn Province in northeastern Vietnam. The river flows in a northeasterly-north direction and ends near the border with Cao Bằng Province.