The Heilongjiang River, which means " the Black Dragon River", gets its name from the color of its water that flows through the densely forested regions covered with the black humus soil. The river has two sources: the southern and the main source is the Ergun River, whose headstream is the Hailar River that originates from the west face of the Greater Hinggan range in Inner Mongolia, and the northern source is the Shilka River, which rises in the eastern foothills of the Kentei Mountains in the north of the Mongolian People's Republic. The two headstreams merge west of Moho to form the Heilongjiang River, which collects the waters of the Songhua and Wusuli as it flows into the Tatar Strait. The Heilongjiang, from the confluence of its two sources to its convergence with the Wusuli at Khabarovsk (Boli) in Russia, is the boundary river between China and Russia. The Heilongjiang has a total length of 4,350 kilometers, of which 2,965 kilometers are in China and Russia border, and a total catchment area of 1,843 million square kilometers, of which 890,000 square kilometers are in China. The trunk stream of the Heilongjiang in China drains an area of 254,769 square kilometers. The Heilongjiang is wide and deep. Its trunk stream, navigable downriver from Moho, is icebound for more than five months in a year. The Songhua River, the largest tributary of the Heilong River is 1,927 kilometers long and drains an area of 545,000 square kilometers.