The major drainage system is the Owyhee River, a tributary of the Snake River. The Owyhee Project, constructed by the Bureau of Reclamation, harnesses the unpredictable Owyhee River to provide water to the fertile soils of the Owyhee and Central Snake River Valleys. In 2008 the valley celebrated the 75th anniversary of the dedication of the Owyhee Dam. In 1925, after studying various reports and p
lans made by the Government engineers, State cooperative boards, and private companies, after conducting further investigation of their own, the Bureau issued a feasibility report recommending the construction of the Owyhee Project. Work began on the storage dam and canal system in 1928, and the first water was delivered to the project lands in 1935. The Owyhee Project was designed to supply water to the entire project area by gravity flow from the Owyhee Reservoir. But, because the Owyhee River's flow is frequently too low to supply the necessary water, privately-constructed pumping plants provide Snake River water to lower-lying project lands. These plants are operated under a 1936 contract between the Bureau of Reclamation and several irrigation districts.
