The Walla Walla River is a tributary of the Columbia River, joining the Columbia just above Wallula Gap in southeastern Washington in the United States. The river flows through Umatilla County, Oregon and Walla Walla County, Washington. Its drainage basin is 1,758 square miles (4,550 km square) in area.
The headwaters of the Walla Walla River lie in the Blue Mountains of northeastern Oregon. The river originates as the North and South Forks of the Walla Walla River. The surrounding forested land holds a network of hiking and mountain-biking trails.
The confluence of the North and South Forks lies east of Milton-Freewater, Oregon. The river flows eastward to reach Milton Freewater, which is built along its banks, and then flows northward through Milton-Freewater. Irrigation water is drawn from the river here and at numerous locations along the river. The Walla Walla River flows southwest of the city of Walla Walla in the Walla Walla valley. Mill Creek, which flows through the city of Walla Walla, joins the Walla Walla river at the Whitman Mission west of the city of Walla Walla.
The Touchet River joins the Walla Walla at the town of Touchet, Washington. The annual mean discharge of the Walla Walla River just below the Touchet River confluence is 1,212 cu ft/s (34.3 m3/s). The maximum recorded discharge was 20,300 cu ft/s (570 m3/s) in 1964. The river enters the Columbia a mile south of the town of Wallula just north of Wallula Gap. The section of the Columbia River is called Wallula Lake, the reservoir impoundment created by McNary Dam.
The Walla Walla River supports populations of spring Chinook salmon, summer steelhead, and bull trout among other species. There is a sport fishery for steelhead in the river. It also holds Channel Catfish and Smallmouth Bass in the summer.