Nam Sam River

Chu River, also known as the Nam Sam River or Nam Xam River, is the largest tributary of Mã River. It originates from Houa peak at 2062m near Xam Neua town, Houaphanh Province in eastern Laos and travels east to meander through the Nghệ An and Thanh Hóa provinces of Vietnam. It joins Mã River on the left in Thiệu Hóa.
The river is 325 km long with a drainage area of about 7,580 km².