McKay Reservoir (Umatilla)

Reachcode: 17070103004024 | Area: 1174.2 acres | Shoreline: 11.6 mi | View on Interactive Map

(From Atlas of Oregon Lakes, Johnson et al. 1985). McKay Dam and Reservoir are located on McKay Creek about seven miles above its confluence with the Umatilla River. The reservoir was developed by the Bureau of Reclamation to furnish a supplementary supply of water to the Stanfield and Westland Irrigation Districts. McKay Dam was originally constructed during 1923-27. It is an earthfill structure, 165 feet high, and impounds a maximum of 70,000 acre feet of water which cover 1316 acres. The Bureau of Reclamation began as early as 1903 to determine the feasility of irrigating lands along the lower Umatilla River. Their studies resulted in the construction of Cold Springs Dam and Reservoir (1906-08) and the establishment of the Umatilla Project. In 1923, construction was started on McKay Dam and Reservoir and was completed in 1927. The Westland Irrigation District was formed to cooperate with the Bureau of Reclamation in utilizingwater stored in McKay Reservoir. Later, the Stanfield Irrigation District was organized to negotiate with the Bureau for storage in McKay Reservoir. The Umatilla Project now consists of three divisions, and furnishes a full supply of irrigation water to 17,348 acres and asupplemental supply to 13,235 acres. The Stanfield and Westland Irrigation Districts, which receive water from McKay, are in the South Division. The Stanfield District is on the east side of the Umatilla River near the town of Stanfield and the Westland District is west of the river near Hermiston. The Bureau of Reclamation continues to operate the reservoir, while the irrigation districts operate their own facilities, and have each contracted for a 30 percent ownership of the storage space in the reservoir. Water is released from the reservoir on request from the districts, and they operate their own canal systems (Bureau of Reclamation 1980).

In addition to the primary purpose of irrigation storage, McKay Reservoir provides auxiliary benefits, specifically for flood control, recreation, and fish and wildlife. McKay Dam is operated on an informal basis for flood control and greatly reduces flows that otherwise would be very damaging. Modification of the spillway section was made in 1978-79 to increase the discharge capacity. This will not prevent damaging flows downstream during an extreme flood event, but it will ensure against a catastrophic flood from dam failure. Recreation at the reservoir, particularly for fishermen, is severely limited by the extreme drawdown required by late summer. Losses of gamefish and destruction of their habitat occurs annually both here and in the Cold Springs Reservoir. The problem is more acute in McKay Reservoir because of low streamflows. There is no supplemental inflow as there is to Cold Springs Reservoir from the Umatilla River. The Oregon Department of Fish and Wildlife stocks McKay with rainbow trout every year, but no minimum pool is guaranteed for their survival. Several times the reservoir has been chemically treated to control species of rough fish. Bass, catfish, bluegills, and crappies have also been stocked and they all provide good fishing at times. Boats can be launched, although no fishing from boats is allowed from April 1 to September 30. There are no camping facilities.

Both the McKay and Cold Springs Reservoir areas are natural wildlife refuges that are heavily used by migrating waterfowl. The McKay Creek National Wildlife Refuge, established in 1927, consists of 515 acres of the water surface and adjacent shoreline. It provides nesting and feeding areas for thousands of Canadian geese, mallards, sandhill cranes, and other birds. About 200 acres of wheat are planted for the waterfowl and upland game birds. The marshland at the upper end of the reservoir where McKay Creek enters is particularly used by the birds. Some 275 acres of the area have been designated as public hunting grounds.

Typical of most reservoirs in the semi-arid country of eastern Oregon, McKay Reservoir is distinctly eutrophic, and although the total phosphorus measurement on 6/24/82 was anomalously low (0.012 mg/1), the reservoir is well enriched with algal nutrients from several sources. As noted, McKay Creek flows through a marshy area, and is nutrient enriched. The abundant waterfowl also contribute nutrients, as does the muddy bottom of the reservoir. Very heavy blue-green algal blooms (Aphanizomenon flos-aquae) develop as early as late spring. On 6/24/82 the surface water temperature was 76 degrees Fahrenheit (24.4 degrees Celsius), which greatly enhances phytoplankton growth rates. On this date, the reservoir was stratified; the thermocline was located at a shallow depth of 13 feet (4 meters). The hypolimnetic dissolved oxygen was slightly less than saturation; however, later in the summer it would be expected to go anoxic. McHugh (1972) also reported an Aphanizomenon flos-aquae bloom in the summer, and he observed predominantly eutrophic diatoms in the winter (Melosira granulata, Synedra ulna). Due to large irrigation water withdrawal during summer, the reservoir area and water depths become greatly reduced, preventing extensive growth of macrophytes.

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