Columbia River - Watershed - Major Tributaries

Major Tributaries

See also: List of tributaries of the Columbia River

The Columbia receives more than 60 significant tributaries. The four largest that empty directly into the Columbia (measured either by discharge or by size of watershed) are the Snake River (mostly in Idaho), the Willamette River (in northwest Oregon), the Kootenay River (mostly in British Columbia), and the Pend Oreille River (mostly in northern Washington and Idaho, also known as the lower part of the Clark Fork). Each of these four averages more than 20,000 cubic feet per second (570 m3/s) and drains an area of more than 20,000 square miles (52,000 km2).

The Snake is by far the largest tributary. Its watershed of 108,000 square miles (280,000 km2) is larger than the state of Idaho. Its discharge is nearly equal to the Columbia's at the rivers' confluence. Compared to the Columbia above the confluence, the Snake is longer (113%), and its drainage basin is larger (104%).

The Pend Oreille river system (including its main tributaries, the Clark Fork and Flathead rivers) is also similar in size to the Columbia at their confluence. Compared to the Columbia River above the two rivers' confluence, the Pend Oreille-Clark-Flathead is nearly as long (about 86%), its basin about three-fourths as large (76%), and its discharge over a third (37%).

Tributary	Average discharge		Drainage basin
	ft3/s	m3/s	mi2	km2
Snake River	56,900	1,610	107,500	278,400
Willamette River	37,400	1,060	11,460	29,680
Kootenay River (Kootenai)	30,650	868	19,420	50,300
Pend Oreille River	26,430	748	25,800	66,800
Cowlitz River	9,140	259	2,586	6,700
Spokane River	7,900	224	6,680	17,300
Lewis River	6,125	173	1,046	2,710
Deschutes River	5,845	166	10,700	27,700
Yakima River	3,542	100	6,150	15,900
Wenatchee River	3,079	87	1,350	3,500
Okanogan River	3,039	86	8,340	21,600
Kettle River	2,925	83	4,200	10,880
Sandy River	2,257	64	508	1,316
John Day River	2,060	58	8,010	20,750