Nam Sam River

Nam Sam River on map

Chu River (name in Vietnam, Vietnamese: Sông Chu) or Nam Sam River (name in Laos) is the largest tributary of Ma River. It originates from Houa peak at 2062 m near Xam Neua town, Houaphanh Province in eastern Laos and travels east to meander through Nghệ An and Thanh Hóa provinces of Vietnam. It joins Ma River on the left in Thiệu Hóa.

The river is 325 km long (165 km in Laos and 160 km in Vietnam) with a drainage area of about 7,580 km² (4,570 km² in Laos and 3,010 km² in Vietnam).

Coordinates: 19°52′52″N 105°45′23″E / 19.8812°N 105.7565°E / 19.8812; 105.7565