Pine Hollow Reservoir
- Wasco County)
(From Atlas of Oregon Lakes, Johnson et al. 1985) Pine Hollow Reservoir is a relatively new impoundment on the east slope of the northern Oregon Cascades, built in the 1960s for the dual purposes of irrigation and recreation. A 65-foot high earthfill dam impounds the waters of Threemile Creek and Pine Hollow Creek and provides storage for about 4800 acre feet of water at a maximum surface area of 228 acres. Construction of the reservoir was the result of a cooperative agreement between the Oregon Department of Fish and Wildlife and the local irrigation district, and the stored water is an important contribution to agricultural activity in the Prineville area.
Because of the network of irrigation ditches in the area, inflow of water from the natural drainage basin accounts for only a small portion of the water in the reservoir. Surrounding land is used primarily for agriculture in the lower reaches of the drainage basin while the upper reaches consist of forested slopes in the Mt. Hood National Forest. The reservoir itself lies on private land just east of the Mt. Hood National Forest boundary. However, public access is permitted from most of the shoreline. According to agreement between the parties that built the reservoir, it is not drained dry each fall as are many of the other small irrigation impoundments in Central and Eastern Oregon. Thus fish are able to survive from year to year; rainbow trout are stocked and provide good angling. There are no visitor services at the reservoir.
The concentrations of ions in the water are surprisingly low for a water body in this semi-arid environment where agriculture is an important land use in the drainage basin. The reservoir is not deep (21 feet mean depth) but does develop a noticeable temperature stratification during the summer. The concentration of phosphorus is moderate, and water transparency is limited. The reservoir is mesotrophic in character.