The Fen River drains the center of Shanxi Province, China. It originates in the Guancen Mountains of Ningwu County in northeast Shanxi, flows southeast into the basin of Taiyuan, and then south through the central valley of Shanxi before turning west to join the Yellow River west of Hejin. The Fen and the Wei Rivers are the two largest tributaries of the Yellow River. The river is 694 kilometers (431 mi) long and drains an area of 39,417 km2 (15,219 sq mi), 25.3% of Shanxi's area. The Fen River is the longest in Shanxi. It is also the second-longest tributary of the Yellow River. Within Taiyuan, the Fen runs from north to south; the prefecture includes one-seventh of the river's course. Source: Wikipedia (en)