John Day River

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.[4][7] However, the steelhead populations are under federal Endangered Species Act (ESA) protections, and the Chinook salmon have been proposed for such protection.

The river was named for John Day, a member of the Pacific Fur Company's overland expedition to the mouth of the Columbia River that left Missouri in 1810. Day struggled through eastern Oregon during the winter of 1811–12. While descending the Columbia River in April 1812, he and Ramsay Crooks were robbed and stripped naked by Native Americans at the mouth of the river that now bears his name, forcing them to hike 80 miles (130 km) back to friendly Umatilla Indians under extreme conditions.

The absence of dams on the river causes its flow to greatly fluctuate throughout the year depending on snowpack and rainfall within the watershed. The highest flow recorded at a gauge on the lower John Day was 43,300 cubic feet per second (1,230 m3/s) on January 2, 1997. The lowest flow was no flow at all, which occurred on September 2, 1966; from August 15 to September 16, 1973; and on nine days in August 1977. The average flow at the gauge is 2,075 cubic feet per second (58.8 m³/s).