The Bitterroot River is a tributary of the Clark Fork River in southwestern Montana, USA. It runs for about 75 miles (121 km) south-to-north through the Bitterroot Valley, from the confluence of its West and East forks near Conner to the Clark Fork near Missoula.
Ravalli County and Missoula County along with the towns along the Bitterroot River, including Hamilton, Stevensville and Missoula, are popular destinations for fly fishing, with rainbow trout being fairly prevalent and with smaller populations of brown trout and cutthroat trout. Although the Bitterroot River passes close by to many residential areas, it is an excellent place for wildlife viewing. Many species of ducks and waterfowl are common along with osprey, bald eagles and heron. Both white-tailed deer and mule deer frequent the river as a source of water and to graze near its banks. The most notable wildlife viewing local along the river is the famous Lee Metcalf National Wildlife Refuge.