The Imnaha River is a 73.3-mile-long (118.0 km) tributary of the Snake River in the U.S. state of Oregon. Flowing generally east near the headwaters and then north through Wallowa County, the entire river is designated Wild and Scenic. It follows a geologic fault to the Snake River, and in addition to land in the Wallowa–Whitman National Forest and private land, its corridor includes parts of three special management areas: the Eagle Cap Wilderness, Hells Canyon National Recreation Area, and Hells Canyon Scenic Byway. The Imnaha flows by the unincorporated community of Imnaha, the only settlement along its course, and enters the Snake River roughly 4 miles (6 km) from the larger river's confluence with the Salmon River of Idaho and 192 miles (309 km) from its confluence with the Columbia River.

The Snake River is a major river in the interior Pacific Northwest region of the United States. About 1,080 miles (1,740 km) long, it is the largest tributary of the Columbia River, which is the largest North American river that empties into the Pacific Ocean. Beginning in Yellowstone National Park, western Wyoming, it flows across the arid Snake River Plain of southern Idaho, the rugged Hells Canyon on the borders of Idaho, Oregon and Washington, and finally the rolling Palouse Hills of southeast Washington. It joins the Columbia River just downstream from the Tri-Cities, Washington, in the southern Columbia Basin.