Owyhee (ō´wīhē), river, c.300 mi (480 km) long, rising in several branches in SW Idaho, N Nev., and SE Oreg. and flowing N across NE Oreg. to the Snake River; named in 1826 for two Hawaiian employees of the Hudson's Bay Company who were killed by Native Americans. After gold and silver were discovered in the region in 1863, there were many mining camps along the river. The Owyhee reclamation project of the U.S. Bureau of Reclamation irrigates a large area W of the Snake River. Owyhee Dam forms a reservoir 52 mi (84 km) long.