evidence: Yalu River, river of northeastern Asia that forms the northwestern boundary between North Korea and the Northeast region (Manchuria) of China. The Chinese provinces of Jilin and Liaoning are bordered by the river. Its length is estimated to be about 500 miles (800 km), and it drains an area of some 12,260 square miles (31,750 square km). From a mountainous source in the Changbai Mountains, the river flows southwestward to drain into Korea Bay (an embayment of the Yellow Sea). The river is an important source of hydroelectric power, is used for transportation (especially of lumber from the rich forests on its banks), and provides fish for the riverine populations. In addition to serving as a political boundary, the Yalu River constitutes a dividing line between Chinese and Korean cultures. It is generally known abroad by its Chinese name, Yalu, instead of by its Korean name, Amnok. According to ancient writing, the Chinese name, which is derived from the characters ya ("duck") and lu ("greenish blue"), is a comparison of the blueness of the river’s waters to the greenish blue of a particular species of domestic duck that inhabits it. The Yalu did not become a political boundary until the Korean-Chinese border was established toward the end of the Korean Koryŏ dynasty in the 14th century. The river played an important political role in the Korean War (1950–53).