Liao (lyou) [key], principal river of NE China, c.900 mi (1,450 km) long, rising in Inner Mongolia and flowing east then south through the fertile Liao alluvial plain to the Gulf of Liaodong. The eastern branch, its main tributary, joins it at the Jilin-Liaoning prov. border. The shallow, silt-laden Liao is navigable for light junks c.400 mi (640 km) upstream. It was the main route into S Manchuria until the construction of the railroad in the early 20th cent. Through sedimentation, the Liao delta has steadily grown.