The Lostine River is a 31.4-mile-long (50.5 km)[1] tributary of the Wallowa River in northeastern Oregon in the United States.[2] It drains a portion of the Eagle Cap Wilderness of the Wallowa Mountains in the Wallowa-Whitman National Forest. It joins the Wallowa River at Wallowa. In 1988, 16 miles (26 km) of the Lostine received National Wild and Scenic River designation.[2]
It rises as two forks, the East Fork (sometimes referred to as East Lostine River) and West Fork (shown on topographic maps as the Lostine River main stem) at elevations of more than 8,000 feet (2,400 m) approximately 15 miles (24 km) south of the city of Lostine and 10 miles (16 km) west-southwest of Joseph. They meet at . It flows generally northward following a large U-shaped canyon. It exits the national forest at an elevation of 3,930 feet (1,200 m) and gradually changes character as it reaches more level terrain which slopes gradually down to 3,000 feet (910 m), where it meets the Wallowa River. The river's flow varies seasonally from about 50 to 1,000 cubic feet per second (1.4 to 28 m3/s).
Irrigation diversions play a significant role in the river, both as input from the Minam Lake and Minam River and diversionary output to the Wallowa River.[3] These water diversions contributed to the end of the local run of coho salmon, and reduced the population of the run of spring chinook salmon to a low of 13 fish in 1999; both had been a historic source of food for the Nez Perce people. Since that year the chinook salmon run has recovered to 800 fish in 2005. An agreement between the farmers, the Nez Perce and the Oregon Water Trust reached in 2005 have led to an effort to preserve the streamflow during the summer, helping the salmon run to survive.[4] Since that year the chinook salmon population has increased to 3,000 fish in 2009.