Thief Valley Reservoir (Baker, Union)

Reachcode: 17050203006118 | Area: 750.8 acres | Shoreline: 10.6 mi | View on Interactive Map

(From Atlas of Oregon Lakes, Johnson et al. 1985)  Thief Valley Reservoir on the Powder River is an irrigation impoundment constructed in 1932 by the Bureau of Reclamation for the Lower Powder River Irrigation District. It is the key component of the lower division of the Baker Project, and serves as a supplemental water supply for about 7300 acres of agricultural land along the Powder River. Phillips Lake, located about 10 miles southeast of Baker, is the principal component of the Upper Division of the Baker Project. Thief Valley is a little valley east of North Powder, and is the site where John Wetherly was hanged in 1864 for stealing mules from an emigrant at Boise; hence the name of the valley and of the reservoir.

The area receives fairly heavy recreational use from hunters, four-wheelers, and fishermen. A portion of the reservoir area has been set aside for recreation use and is administered by Union County. Camping, picnicking, and boat launching and mooring facilities have been constructed. The reservoir has developed a reputation for good fishing for trout, largemouth bass, and black crappie, all of which have been planted. Unfortunately, there is also an abundance of rough fish. The headwater portion of the drainage basin is within the Wallowa-Whitman National Forest, while the lower reaches are a mixture of private and federal (Bureau of Land Management) land used mostly for grazing. The shoreline of the reservoir, except for the county recreation area, is in federal ownership.

Thief Valley Reservoir is approximately two miles long, one-half mile wide, and covers an area of 740 acres when full. Since the construction of Mason Dam (Phillips Lake) upstream, surface area at minimum pool is approximately 200 acres. At full pool, maximum depth is 38 feet and much of the reservoir is less than 20 feet deep. There are frequent strong afternoon winds which cause resuspension of bottom sediment which increases turbidity and clouds the water.

The climate of the region is dry, and the concentrations of ions in the water are fairly high. Conductivity and alkalinity are above average for eastern Oregon reservoirs, and pH is frequently above 8. There is a noticeable tendency for oxygen depletion in the hypolimnion. However, most of the reservoir is only weakly stratified and frequently mixed. The concentration of phosphorus is high, and water transparency limited. Algae (Aphanizomenon) bloom in the reservoir during the summer, causing high chlorophyl concentrations. However, the inorganic turbidity probably reduces light availability and thereby limits algal blooms somewhat. Because it is supplied with nutrients and is shallow, Thief Valley Reservoir is eutrophic.


The list below includes results of zebra and quagga mussels surveys conducted by the Center for Lakes and Reservoirs and other agencies. The results "non-detect" and "results pending" indicate that surveys for zebra and quagga mussels were conducted, but none were detected or results are pending. For more details on zebra and quagga mussel monitoring, please visit the Online Mussel Monitoring Map.

Date Status/Species Source
July 18, 2012 non detect Portland State University
July 17, 2012 non detect Portland State University
No plant data available.
0/0