The Salmon River is located in Idaho in the northwestern United States. The Salmon is also known as The River of No Return. It flows for 425 miles (684 km) through central Idaho, draining a rugged, thinly populated watershed of 14,000 square miles (36,260 km2) and dropping more than 7,000 feet (2,134 m) between its headwaters, near Galena Summit above the Sawtooth Valley in the Sawtooth National Recreation Area, and its confluence with the Snake River. Measured at White Bird, its average discharge is 11,060 cubic feet (313 m3) per second. It is one of the largest rivers in the continental United States without a single dam on its main stem.

Cities located along the Salmon River include Stanley, Clayton, Challis, Salmon, Riggins, and White Bird. Redfish Lake and Little Redfish Lake near Stanley, which flow into the river via Redfish Lake Creek, are the terminus of the longest Pacific sockeye salmon migration in North America.

North of Salmon, the river is joined by the North Fork, before turning west into over 200 miles of continuous canyons through the Salmon River and Clearwater Mountains – some of the most rugged and isolated terrain in the contiguous United States. Exhibiting upwards of 7,000 feet of vertical relief, the Salmon River canyons are some of the deepest in the US, surpassing the Grand Canyon and second only to the Snake River's Hells Canyon on the Idaho–Oregon border. Here, the river is joined by its two largest tributaries, the Middle Fork and South Fork.

Several national forests and Sawtooth National Recreation Area provide for numerous recreation opportunities within the river's watershed. Two segments (the Middle Fork and Main Fork) are protected as National Wild and Scenic Rivers. The Middle Fork was one of the original eight rivers designated in 1968, and is often considered the "crown jewel" of the Wild and Scenic system.

The Salmon is a popular destination for whitewater kayaking, canoeing and rafting. The canyons of the Salmon allow for magnificent views of the complex geology of the region. The Frank Church-River of No Return Wilderness Area includes one of the deepest canyons in the continental United States, which at roughly 7,000 feet (2,100 m) of vertical relief, is deeper than the Grand Canyon.

The Salmon River historically produced 45% percent of all the steelhead (trout) and 45 percent of all the spring and summer chinook salmon in the entire Columbia River Basin. The Salmon River basin contains most (up to 70 percent) of the remaining salmon and steelhead habitat in the Columbia River Basin. Despite the abundant salmon habitat in the river, these fish have been declining, in large part because of the effects of four federal reservoirs and dams on the lower Snake and Columbia rivers.