river, southern North Korea, rising in the Nangnim Mountains in Hamgyŏng-nam do (province). It flows 273 miles (439 km) southwestward to enter Korea Bay, an arm of the Yellow Sea, at Namp'o. With its tributaries it forms a drainage basin of 7,855 square miles (20,344 square km). Because of its deep water and the tidal influence of the Yellow Sea, it is useful for water transportation, and many river ports, such as P'yŏngyang, have been developed along its course. It is navigable for ships of 4,000 tons to Songnim and for ships of 2,000 tons to 40 miles (65 km) from the mouth of the river. Farther upstream it is extensively utilized for irrigation.