Marion/Linn County

Willamette/Sandy Basin

Location Area 3,580 acres (1,448.8 hect) Elevation 1,569 ft (478.2 m) Type reservoir Use multipurpose Location 46 miles southeast of Salem Access adjacent to Ore Hw y 22 USGS Quad Detroit (24K), (100K) Coordinates 44˚ 43' 17" N, 122˚ 14' 55" W USPLSS tow nship 10S, range 05E, section 07

Detroit Lake is a large storage reservoir on the North Fork of the Santiam River, one of 13 multipurpose, water resource projects in the basin constructed and operated by the U. S. Army Corps of Engineers. The project became operational in 1953, at the same time as Big Cliff Lake, a reregulating reservoir (surge basin) immediately downstream from Detroit Lake. Detroit Lake was intended primarily for flood control and power generation, but the large reservoir has become one of the major recreation resources in western . Nearly half a million people visit each year, most of them coming during the busy summer months when high water levels are maintained. It is a beautiful, nine-mile long impoundment Source: Oregon Department of Transportation, no date. View looking south. which twists its way through the western slopes of the Cascade Mountains below Mt. Jefferson. Three main arms branch off the main stem, and the flooded tributaries reach deeply ` Drainage Basin Characteristics into the mountainous and forested terrain. Shoreline slopes are quite steep and, as a result, very little land around the lake is suited for development. There are several patches of private Area 423.0 sq mi (1,095.6 sq km) Relief steep Precip 65-120 in (165-305 cm ) land on these slopes. The town of Detroit, from which Detroit Lake derives its name (many Agriculture Michigan people have lived in the area), lies on the shoreline where the Land Forest Range Water Irrig Non Irrig Urban Other joins the lake. Us e % 96.3 0.2 1.6 - - 0.1 1.9 Note s Other - Rock outcrops The lower portion of the drainage basin consists of andesite lava flows mixed with ash beds, Lake Morphometry M axim um Average all deeply incised and dissected by stream action. Some slope failure has occurred in parts of Area 3,580.0 acres (1,448.8 hect) Depth 440 ft (134.1 m) 121ft (36.9 M) the basin but turbidity has not been a problem as in some other area reservoirs (for example, Ave/Max Depth Ratio 0.280 Volume 455,000 acre ft (562.06 cu hm ) Hills Creek Lake). A granitic intrusion, a fairly uncommon rock type for this part of the state, Shoal area 5% Volum e factor 1.10 Shape factor 4.10 crops up by Detroit . It is a mass of andesitic magma that did not reach the surface and Length of Shoreline 35.5 mi (57.1 km) Retention tim e 3 mo cooled more slowly at depth. Possibly it represents the core of an old volcano that fed the Notes Area, volume, and depth from U.S. Army Corps of Engineers surrounding volcanoes during the buildup of the Cascades about 25 million years ago. Most of the large drainage basin is covered with a coniferous forest managed by the Willamette W ater Quality National Forest. Douglas fir is the dominant species in the lower portion of the drainage Trophic status mesotrophic, no evidence of cultural enrichment basin, grading into hemlock and true firs at the higher elevations. Sam ple date 09/15/82 Tem p 64.9F (18.3C) Diss. Oxygen (m g/l) 9.5 Fishing leads the list of recreational activities at Detroit Lake, with an estimated 100,000 Transparency 18.4 ft (5.6 m) Phosp (mg/l) 0.017 Cholorophyl a (mg/l) 1.7 angling-days and a catch of 200,000 fish per year. About 85 percent of the catch is rainbow Alkalinity 14 Conductivity (umhos/cm) 34 pH - trout; these are stocked in large numbers by the Oregon Department of Fish and Wildlife, Major Na K Ca Mg Cl SO4 with legal-size and fingerlings added monthly in summer. Piety Knob, a large island rising Ions 2.2 0.5 3.5 1.0 0.6 0.2 450 feet from the center of the reservoir, is adjacent to a favorite trolling area. Brook trout, Notes - cutthroat trout, kokanee, and bullhead supplement the trout fishery, and chinook salmon have 11/07/82 51.8F (11.0C) occasionally been stocked. Since the 463-foot high concrete dam presents an effective barrier Sam ple date Tem p Diss. Oxygen (m g/l) - to migrating adult salmon and steelhead, these fish are intercepted six miles downstream at Transparency - Phosp (mg/l) 0.028 Cholorophyl a (mg/l) 2.9 7.1 Minto Station. Eggs are artificially fertilized here and taken upstream to Marion Forks Alkalinity 14 Conductivity (umhos/cm) 34 pH Hatchery, where the fingerlings are released. Unfortunately, the Minto facility has failed to Major Na K Ca Mg Cl SO4 attract sufficient numbers of chinook because of low-temperature hydropower releases from Ions 2.4 0.8 3.5 1.1 0.7 0.1 Notes - Detroit Lake which tend to hold water temperatures well below the optional temperature range for chinook migration (Larson 1980). Detroit Lake also receives some of the heaviest pleasure boating lake is mesotrophic or moderately productive. The concentration of phosphorus suggests that use in the state. Based on the total number of boating days estimated for 1975, this was the the lake is eutrophic; however, the lake is quite deep and the phosphorus in the third "most used" lake in the state, following coastal Tenmile Lake and Diamond Lake lake evidently does not stimulate eutrophic conditions. Overall, Detroit Lake is mesotrophic, (Frenkel 1975). Five boat ramps and two marinas help make it a very popular water-skiing although at the low end. There is no evidence of cultural enrichment from the high amount of spot. One campground, located on Piety Knob, can be reached only by boat. Three other recreational use. The phytoplankton is composed primarily of four algal species. campgrounds, including the large Detroit State Park on the north shore, provide over 200 tent Rhodomonas minuta was always dominant in the samples collected in 1982; its occurrence is and trailer spots around the lake. Two marinas in town offer boat rentals, moorage, and other not associated with any particular trophic state. Fragilaria crotonensis, and to a lesser extent accommodations. Anabaena, are common, and both indicate mesotrophic to eutrophic conditions. Cryptomonas erosa does not indicate any trophic state, as it is equally common in oligotrophic to eutrophic The water level in Detroit Lake varies throughout the year, a pattern typical of other storage lakes. The total phytoplankton densities are typical of mesotrophic lakes. impoundments in the Willamette Valley. It is a response to seasonal patterns of precipitation and'runoff, and also to downstream requirements and power demands. From 1 December until 31 January, which is the major flood period, the volume of water is about one-half the maximum to allow for storage of flood waters. During late winter and spring, surface runoff fills the reservoir to near capacity, except during drier years. Until August, it is kept at a fairly constant high level, coincident with the recreation season. August through November is the season during which the water is gradually drawn back down to the minimum flood control elevation. This minimum level is 100 feet below full pool elevation and the surface area of the lake is about one-half of the area at full pool. In fall, the released water is used primarily for power production, and two generator units provide 100 megawatts of peak electrical output.

Detroit Lake develops a pronounced thermal stratification with surface water as warm as 68 degrees Fahrenheit (20 degrees Celsius) in the summer, whereas water temperature below 100 feet does not exceed 50 degrees Fahrenheit (10 degrees Celsius). Major ion concentrations arelow, as is characteristic of Cascade reservoirs, and oxygen is near saturation at all depths. Chlorophyl concentrations and water transparency indicate that the

70 Atlas of Oregon Lakes

Source: US Forest Service, 1974. Vertical photograph.

Photo Captions

1. Detroit Lake 2. Big Cliff Lake 3. Dam 4. Oregon Hwy. 22 5. Detroit (town)

Lake Reports 71