The John Day River is a tributary of the Columbia River, approximately 284 miles (457 km) long, in northeastern Oregon in the United States. It is known as the Mah-Hah River by the Cayuse people, the original inhabitants of the region. Undammed along its entire length, the river is the fourth longest free-flowing river in the contiguous United States. There is extensive use of its waters for irrigation. Its course furnishes habitat for diverse species, including wild steelhead and Chinook salmon runs. However, the steelhead populations are under federal Endangered Species Act (ESA) protections, and the Chinook salmon have been proposed for such protection.