Cold Springs Reservoir
- Umatilla County)
(From Atlas of Oregon Lakes, Johnson et al. 1985). Cold Springs Reservoir is a large irrigation impoundment near Hermiston, located in the Cold Springs National Wildlife Refuge. Established in 1909, the Refuge with its tree-lined reservoir lies in sharp contrast with its desert surroundings. It is an important wintering and nesting area for more than a dozen species of migratory waterfowl. The Refuge encompasses 3,117 acres and is cooperatively managed by the U.S. Fish and Wildlife Service, the Bureau of Reclamation, and the Hermiston Irrigation District. The reservoir was formed by construction of a dam across Cold Springs Wash in 1908 by the Bureau of Reclamation, although it did not fill until 1911. At full pool the reservoir covers over 1500 acres and has a capacity of about 50,000 acre-feet. The flow of Cold Springs Wash is insufficient to fill the reservoir, and the major supply is spring runoff from the Umatilla River delivered by the Umatilla Project feed canal. Waters from the reservoir serve the irrigation needs of the local area, and as withdrawals are made through the summer, water levels drop rapidly. By late August, an average of 200 acres of water remain at minimum pool. The lake bed exposed during the drawdown produces an abundance of vegetation which is utilized by a variety of wildlife.
Recreational activities in the area include hunting, birdwatching, and fishing. The reservoir was treated in 1967 to eliminate rough fish, at the same time that the Umatilla River was treated. It has since been stocked with largemouth bass, bluegill, and crappie. Crappie fishing in the spring is particularly good. Brown bullheads have also flourished. Boats can be used, but no motors are allowed, and launching is difficult because of the fluctuating water levels and exposed mudflats. There is no overnight camping near the reservoir.
The basin shape is characteristic of reservoirs constructed in areas of relatively shallow relief. The maximum depth just behind the dam is 71 feet, and average depth is 32 feet. There are two large shallow arms, Despair Gulch arm to the southeast and Cold Springs Canyon arm to the northeast. Hypereutrophic Cold Springs Reservoir is easily one of the most eutrophic bodies of water in the state, and a number of forces act in concert to keep it eutrophic. The major ion concentrations, alkalinity, and conductivity are all above average, even for reservoirs in eastern Oregon. The local climate is dry and there is not a great deal of runoff to dilute weathering products from the drainage basin. The concentration of phosphorus is very high, and more than enough to provoke algal blooms. Some of the phosphorus no doubt accompanies the major ions derived from the drainage basin. In addition, there is extensive agriculture around the reservoir and very large populations of overwintering waterfowl, both of which contribute additional phosphorus. The reservoir is too shallow to stratify, thus keeping nutrients continuously in circulation. As a consequence, there are frequent dense blooms of phytoplankton, giving rise to very high concentrations of chlorophyl and very restricted water transparency. In summary, because of the shallow mean depth and the generous supply of nutrients Cold Springs Reservoir is unavoidably hypereutrophic.