Owyhee River Wilderness, Nature reserve in Owyhee County, United States.

Owyhee River Wilderness is a federally protected nature reserve in the high desert of southwestern Idaho, close to the Oregon border. The terrain is shaped by deep river canyons cut into dark basalt rock, wide open plateaus, and dry valley floors crossed by the Owyhee River.

The area was formally designated as wilderness in 2009 through a federal law that placed the land under permanent protection. Before that, the land had been managed by federal agencies for decades without any formal wilderness designation.

The name Owyhee comes from an old spelling of Hawaii, linked to Hawaiian fur trappers who worked the region in the early 1800s. Today the reserve is managed by the Bureau of Land Management, and about 67.3 miles of the Owyhee River are classified as a wild river. Camping, fishing and seasonal hunting are allowed with the proper permit, while motorized and mechanical equipment, bicycles included, are banned.

Reaching most parts of the reserve requires a high-clearance four-wheel-drive vehicle, as roads are unpaved and often rough. Carrying water, food, and emergency supplies is important because the nearest towns can take several hours to reach.

The Owyhee River Wilderness is the second-largest U.S. wilderness area outside a national forest, park, or wildlife refuge; only the BLM's Black Rock Desert Wilderness is larger. It covers 51.7% of the 517,025 acres of Idaho wilderness added by the 2009 Omnibus Public Land Management Act.