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Owyhee Project Brochure (911 KB) (pdf)
Owyhee Project History (55 KB) (pdf)
General Description| Plan| Development| Benefits

General Description

The Owyhee Project lies west of the Snake River in Malheur County, Oregon, and Owyhee County, Idaho. Principal towns in the area are Homedale, Idaho, and Adrian, Nyssa, and Ontario, Oregon. The project furnishes a full irrigation water supply to over 105,000 acres of land lying along the west side of the Snake River in eastern Oregon and southwestern Idaho. An additional 13,000 acres are furnished supplemental water. About 72 percent of the lands are in Oregon, and 28 percent in Idaho. Irrigable lands are divided into the Mitchell Butte, Dead Ox Flat, and Succor Creek Divisions. The key feature of the project is Owyhee Dam, on the Owyhee River about 11 miles southwest of Adrian, Oregon, which acts as both a storage and diversion structure. Project works also include canals, pipelines, tunnels, 9 pumping plants, laterals and drains.

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The Owyhee River Basin above Owyhee Dam contains 11,160 square miles and has an average runoff of about 760,000 acre-feet. Water for irrigation of project lands is both stored in Lake Owyhee and pumped directly from the Snake River. The water is released from Lake Owyhee through a 3.5-mile tunnel to Tunnel Canyon where the North and South Canals have their headings. The North Canal distributes water to the Mitchell Butte and Dead Ox Flat Divisions. The South Canal distributes water south to the Succor Creek Division.

Originally, the irrigation works were designed to supply water to the entire project by gravity from Lake Owyhee. Because of the irregular flow of the Owyhee River, storage of a 2-year water supply is advisable. Pumping water from the Snake River for lower lying lands makes this possible. A contract executed in 1936 provides for the operation of existing pumping plants to irrigate from 30,000 to 35,000 acres.

Facility Descriptions

Owyhee Dam

Owyhee Dam is a concrete, thick-arch structure which was designed to carry about three-fourths of the water load by arch action, and the remainder by gravity action. The dam rises 417 feet above foundation in the river section, and 530 feet above the low point of the excavated fault zone. At the time of its construction, Owyhee ranked as the world`s highest dam. The arch section is 623 feet long, and a gravity tangent extends 210 feet to the right abutment. The total capacity of Lake Owyhee is 1,120,000 acre-feet (active 715,000 acre-feet).

Owyhee Dam became a proving ground for theories being developed to assist with the design and construction of Hoover Dam, whose unprecedented size - it would tower more than 300 feet higher than Owyhee - required totally new construction methods. The trial load method of design, developed first for Pathfinder and Buffalo Bill Dams, was refined in the design of Owyhee Dam and, later, Hoover Dam. Cooling methods, necessary to remove excess heat of cement hydration from mass concrete and bring a dam to stable temperatures, were carefully studied. A 28-foot-square section extending through the dam was cooled artificially by circulating river water through 1-inch pipes spaced at 4-foot intervals.

Water for irrigation is diverted through a horseshoe-type tunnel 16 feet 7 inches in diameter and 3.5 miles long. This tunnel heads in the reservoir 80 feet below normal maximum water surface.

The needle valves in the outlet works were replaced by the jet flow gates in 1991 as a part of an operation and maintenance modifications program.

North Canal

This canal extends from the diversion works, 3.5 miles from Owyhee Dam, northward 61.5 miles to the Snake River near Weiser, Idaho. The diversion capacity is 1,190 cubic feet per second. The canal contains several siphons and tunnels. The most noteworthy structure is the Malheur River Siphon, which carries water from the Mitchell Butte Division across the Malheur Valley to the Dead Ox Flat Division. It is an 80-inch steel pipe siphon approximately 4.3 miles long with a monolithic concrete pipe section at each end. The design capacity of the siphon is 325 cubic feet per second.

South Canal

The South Canal extends from the diversion works near Owyhee Dam through a 5-mile tunnel and then southward 37 miles to the Snake River south of Marsing, Idaho. The diversion capacity of the canal is 490 cubic feet per second.

Pumping Plants

Dead Ox Pumping Plant, on the Snake River about 5 miles north of Payette, Idaho, pumps water to several irrigation districts in the Dead Ox Flat Division. The plant has five pump units with a total capacity of 176 cubic feet per second.

Owyhee Ditch and Ontario-Nyssa Pumping Plants, on the Snake River 5 miles south of Nyssa, Oregon, pump water to the former Ontario-Nyssa Irrigation District area and the Owyhee Ditch Company in the Mitchell Butte Division. The Owyhee Ditch Pumping Plant has a capacity of 222 cubic feet per second and the Ontario-Nyssa Pumping Plant a capacity of 130 cubic feet per second.

Gem Pumping Plant, 2 miles south of Marsing, Idaho, pumps water from the Snake River to the Gem Irrigation District in the Succor Creek Division. It has a capacity of 334 cubic feet per second.

Power Distribution System

Power from the Southern Idaho Federal Power System is transmitted over lines of a private power company to various points on the Owyhee Project. A project transmission line extends 19.4 miles from Ontario-Nyssa substation at Dunaway, Oregon, to Owyhee Dam.

Non Federal Powerplants

In the 1980s, the water users began pursuing development of hydroelectric power generating facilities on the Owyhee Project and obtained Federal Energy Regulatory Commission licenses to construct and operate three powerplants. These included a 5,000 kilowatt powerplant at Owyhee Dam, using power outlet facilities installed during construction, an 8,000 kilowatt powerplant at Tunnel No. 1, the major diversion works for the project, and a 2,000 kilowatt powerplant on the Mitchell Butte Lateral. These powerplants were placed in operation between 1985 and 1993.

Operating Agencies

Project works, except Owyhee Dam and related works which were retained and operated by the Bureau of Reclamation, were transferred to the water users (represented by the North and South Boards of Control) in 1952 for operation and maintenance. Two years later, Owyhee Dam and related works also were transferred to a Joint Committee comprised of representatives of the North and South Boards of Control for operation and maintenance. On July 14, 1989, all irrigation entities of the North Board of Control merged into the Owyhee Irrigation District and the North Board of Control was dissolved. Owyhee Dam is now operated by the Owyhee Irrigation District in cooperation with the South Board of Control.

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Scouts, trappers, and traders visited the project lands in the early part of the 19th century. Permanent settlers arrived about 60 years later. At the beginning of the 20th century, irrigation in the project area was limited to about 6,000 acres from Owyhee Ditch, diverted from the Owyhee River, and to smaller acreages from Wilson Ditch, the Snake, and individual diversions from Succor Creek. Later, private organizations became interested in developing storage to provide adequate late-season water and to irrigate additional lands at higher elevations. Several damsites were investigated and various irrigation plans considered, but the inaccessibility of the sites made construction costs prohibitive.


From 1903 to 1905, the Reclamation Service made topographic surveys of the irrigable lands in the Owyhee River Basin and of possible reservoir sites. During the following years several reports were made by Government engineers, State cooperative boards, and private companies. After studying various plans and making intensive investigations, the Bureau of Reclamation issued a feasibility report in January 1925 that recommended construction of the project substantially as it has been developed.


Construction of the project was found feasible by the Secretary of the Interior on October 9, 1926, and approved by the President on October 12, 1926 under the provisions of section 4 of the Act of June 10, 1910 (36 Stat. 836) and subsection B of section 4 of the Act of December 5, 1924 (43 Stat. 702). The authorized purpose of the Owyhee Project is irrigation.


Contracts were awarded and work started on the storage dam and canal system in 1928. The first water from constructed works was delivered to the project lands in 1935, and the lateral system was extended to the last irrigation area in 1939.

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The fertile lands and favorable climate, combined with a good supply of irrigation water, make possible the production of abundant crops on the Owyhee Project, principally grain, hay, pasture, sugar beets, potatoes, onions, sweet corn, and alfalfa seed. Livestock and dairy products contribute to the returns from the land.

Flood Control

Flood control criteria has been developed, but it is informal and advisory only. Under these criteria, a minimum of 70,000 acre-feet of space is maintained in Owyhee Reservoir through February and more space is maintained beginning in January if the inflow forecast is large.

The Owyhee Reservoir has 100,000 acre feet of capacity assigned to flood control. The Owyhee Project has provided an accumulated $33,010,000 in flood control benefits from 1950 to 1998.

Recreation, Fish & Wildlife

Owyhee Reservoir is a long, narrow reservoir with about 150 miles of shoreline, located in a canyon of rugged and spectacular beauty. The lake is in a remote area but, because of an excellent warm-water fishery, it experiences heavy recreational use. Lands around the reservoir are mostly public lands under control of the Bureau of Land Management. Boat ramps are provided at four locations, two operated by the Oregon State Parks system, and two operated by Malheur County Waterworks. The lake also provides excellent waterfowl hunting, and the surrounding hills and canyons offer many opportunities for the pursuit of upland game birds. A variety of wildlife may be observed in the reservoir area, including wild horses, bighorn sheep, golden eagles, pelicans, and cormorants.

Endangered Species Act

The Pacific Northwest Region consults with the NOAA Fisheries and the US Fish and Wildlife Service to ensure that project operations and other activities do not jeopardize ESA-listed species or their critical habitats. Fish and Wildlife Service (FWS) and National Marine Fisheries Service (NMFS) provided Biological Opinions on Reclamation's Operations and Maintenance of 12 projects and associated facilties in the Snake River Basin above Lower Brownlee Reservoir. The Owyhee Project is one of the 12 projects covered in the Opinions.

If conditions don't change these Opinions should be valid through 2035.

For more information on ESA related activies please go to:

For more information on the fish and wildlife program, please go to:

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Last updated: Jan 03, 2013