The Da River, also known as Black River, is located in northwestern Vietnam. Its source is in Yunnan province of China. From China, the river’s course passes through the Vietnamese provinces of Lai Chau, Son La and Hoa Binh.
The Black River is the most important tributary of the Red River, which it joins in Tam Nong District near Viet Tri in Phu Tho Province. It also forms part of the border between Phu Tho Province and Hanoi.
Nearly 500 miles (800 km) long, the river rises in central Yunnan province in southwestern China and flows southeastward into northwestern Vietnam on a course parallel to the Red River. Near the city of Hoa Binh, 37 miles (60 km) southwest of Hanoi, the Black River is dammed to form a reservoir that is the largest in Vietnam.
The Hoa Binh Dam went into operation in 1988, though work on its hydroelectric generating station was not completed until 1994. The dam’s 1,920-megawatt power plant generates a significant portion of Vietnam’s total electricity requirement. After passing the dam, the Black River turns sharply north and unites with the Red River about 35 miles (55 km) northwest of Hanoi.