The Yahara River is a tributary of the Rock River, about 45 mi (70 km) long, in southern Wisconsin in the United States. Via the Rock River, it is part of the watershed of the Mississippi River. The Yahara links the lakes upon which the city of Madison was built.
The river rises in northern Dane County and initially flows southwardly past DeForest and Windsor into Lake Mendota in Madison, below which it turns southeastward and flows through Lake Monona, Lake Waubesa and Lake Kegonsa and passes the communities of Monona, McFarland and Stoughton. It joins the Rock River in northern Rock County, 9 mi (14.5 km) north of Janesville.
The U.S. Board on Geographic Names settled on "Yahara River" as the stream's name in 1903. According to the Geographic Names Information System, it has also been known historically as "Catfish River," "Gahara River," and "Myan-mek."