Prineville Reservoir (Crook)

Reachcode: 17070304003611 | Area: 2859.6 acres | Shoreline: 41.2 mi | View on Interactive Map

(From Atlas of Oregon Lakes, Johnson et al. 1985). Prineville Reservoir is one of the major components of the Bureau of Reclamation's Crooked River Project which lies north and west of Prineville, Oregon. Project features include Arthur it. Bowman Dam and Prineville Reservoir, Ochoco Dam and Reservoir, a diversion canal and headworks on the Crooked River, Lytle Creek Diversion Dam and Wasteway, two major pumping plants, nine small pumping plants, the Ochoco Main Canal, and distribution canals. The project provides several benefits to this portion of Oregon: more than 20,000 acres of land are irrigated by waters stored in the two reservoirs; flood protection is provided for Prineville and adjacent farmland areas; recreation use of the reservoirs has been heavy; and the upper end of Prineville Reservoir has been designated a wildlife management area, a 3800 acre area of land and water that provides habitat for a variety of wildlife including numerous species of waterfowl.

Ochoco Dam and Reservoir were constructed in 1918-20 and rehabilitated by the Bureau of Reclamation in 1949-50. Construction of Arthur R. Bowman Dam (originally known as Prineville Dam) began in 1958 and was completed in 1961. It is an earthfill structure, 245 feet high, on the Crooked River about 20 miles upstream from Prineville. Prineville Reservoir has a total capacity of about 160,000 acre feet and a water surface area of over 3000 acres at full pool elevation. It is a long narrow impoundment conforming to the shape of the steep-sided Crooked River Canyon. It extends 18 miles upstream, with 41 miles of shoreline. The Crooked River is the principal source of water, supplying more than 90 percent of the inflow. Bear Creek, entering from the south, is the major tributary, and there are several other small, intermittent streams that enter the reservoir directly.

The drainage basin above the dam is an area of about 2700 square miles, although about 20 percent of this is interior drainage that does not contribute. It consists essentially of the eastern two-thirds of Crook County, with minor acreages in other counties. Elevations range from 3235 feet above sea level at the dam to over 6000 feet in the Ochoco and Maury Mountains. There are concurrent variations in climate, vegetation, and land use. Most of the area is a semi-arid rangeland, with forest cover at higher elevations. There is also a substantial amount of irrigated agricultural land flanking the lower reaches of the Crooked River. Geology of the area is quite variable and includes some of the oldest bedrock in Oregon. Large portions of the basin are underlain by basic lavas and tuffs, while much older marine sedimentary formations underlie the headwaters of the Crooked River.

Prineville Reservoir has become one of the major recreation resources of Central Oregon. This development was unanticipated and occurred because a number of good water years permitted the maintenance of a relatively full reservoir. Crook County administers the shoreline along the lower reach of the reservoir for public recreation and has constructed several boat ramps and a primitive campground. The county has subleased two areas, one to the state of Oregon for a state park and the other to a concessionaire for development of a resort. Prineville State Park consists of a developed campground with shower facilities, a boat-launching ramp, a marina, and a day-use area. The campground is one of the most heavily used in the state. The resort operated by the concessionaire includes a motel, a marina, a beach, rental boats, and a combined store and restaurant. Two residential subdivisions have been developed on private lands adjacent to the reservoir area and several developments of both residential and recreational homes have been built nearby. Fishermen have had very good success at Prineville Reservoir, which is stocked regularly with rainbow trout and largemouth bass. Catfish are also present in the lake and some cutthroat trout have been stocked in recent years.

The limnological characteristics are heavily influenced by the presence of inorganic turbidity, a problem attributed to the siting of the reservoir. Turbidity is a water quality problem throughout the Crooked River system, and it affects the reservoir and reservoir releases. As noted, it is a large drainage basin and contains diverse soil and rock types with a variety of land use activities. Many of these soil types are prone to erosion and the generation of turbid runoff. Land use activities accelerate the erosion of fine soil and sediment; logging practices, fire prevention techniques, road building, and cattle grazing all contribute to increased sediment discharge to the river. Perimeter erosion around the shoreline is also a factor. There are many exposed points and headlands and the waters near the shoreline are particularly turbid, a situation that is aggravated during the months of heavy' recreational use. Heavy boat traffic creates surface waves which accelerate erosion along the shoreline; the waves also resuspend bottom sediments from the exposed shallow areas of the reservoir. Sediment transport to the reservoir is highly dependent on the surface runoff regime and therefore quite variable throughout the year. The total mass of sediment transported to the reservoir may exceed one half million tons per year. Most of it is very fine clays of the montmorillite group. Because of the fineness of the soil particles and the lack of chemicals in the water to make particles flocculate, the reservoir remains turbid for long periods after runoff has entered. The soil particles settle towards the bottom eventually, but since the outlet is near the bottom some of the most turbid water is released into the Crooked River. Identification of specific sources of the clay has not been made and until revegetation of these sources occurs, the turbidity problem will persist.

The concentrations of major ions and the conductivity in Prineville Reservoir is greater than average for reservoirs in Oregon. The reservoir develops a distinct thermal stratification during the summer, with a thermocline at 33 to 50 feet (10 to 15 meters) depth. The epilimnion gradually becomes somewhat more transparent over the summer, but the hypolimnion remains turbid. The highest water transparency (Secchi disk depth of 10 feet; 3 meters) observed in 1982 occurred in August; during most of the year water transparency is limited to 5 feet (1.5 meters) or less by the inorganic turbidity. The inorganic turbidity may retard the growth of planktonic algae. Most reservoirs in Central Oregon support summer blooms of the blue-green alga Aphanizomenon. Aphanizomenon blooms occur in Prineville Reservoir, but less frequently than in other similar reservoirs. The timing of these blooms is also different in Prineville Reservoir than in other eastern Oregon reservoirs. Phytoplankton measurements in this study, as well as those made by McHugh (1972), show that the Aphanizomenon bloom does not develop until autumn. The reason for this delay is unknown, but may be related to the turbidity. In November 1982, Anabaena was almost as abundant as Aphanizomenon. (Note: Rhodomonas minuta, although numerically dominant, is quite small and thus contributes little to the total biomass.) During spring and summer, the phytoplankton is dominated by diatoms; most of these diatoms are periphytic (that is, growing attached to a substrate), and are not typical of lakes. These diatoms may be associated with the suspended clays that are derived from the drainage basin. The chlorophyl concentration and especially the phytoplankton densities are unusually low. In August, 1982, the total phytoplankton density was only 6 per ml.

Macrophytes in Prineville Reservoir are absent or scarce due to rocky littoral areas, water level fluctuations, and limited water transparency. The reservoir is classified as eutrophic primarily because of the limited light transparency and the elevated Concentrations of phosphorus. Chlorophyl concentrations are consistently low compared with the phosphorus and water transparency data. The low chlorophyl concentrations and reduced frequency of plankton blooms suggest light limitation.

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
Aug. 29, 2013 non detect Portland State University
Aug. 28, 2013 non detect Portland State University
Aug. 1, 2013 non detect Portland State University
Sept. 13, 2012 non detect Portland State University
Aug. 23, 2012 non detect Portland State University
Aug. 22, 2012 non detect Portland State University
Aug. 21, 2012 non detect Portland State University
Sept. 14, 2010 non detect Oregon Dept of Fish and Wildlife
Aug. 13, 2010 results pending Portland State University
July 23, 2010 results pending Portland State University
No plant data available.