High Quality Content by WIKIPEDIA articles! The John Day River is a tributary of the Columbia River, approximately 281 miles (452 km) long, in northeastern Oregon in the United States. Undammed along its entire length, the river is the third longest free-flowing river in the conterminous United States. There is extensive use of its waters for irrigation. Its free-flowing course furnishes habitat for diverse species, including wild steelhead runs. However, the steelhead populations are under federal endangered species protections, and chinook salmon have been proposed for Environmentally Sensitive Area (ESA) protection.