Loon Lake Dam

Loon Lake
Company type	Reservoir
Industry	Hydroelectric power, Recreation
Founded	1962
Headquarters	El Dorado County, United States
Area served	Eldorado National Forest, California
Products	Hydroelectric power, Recreational facilities (camping, boating, fishing)
Parent	Sacramento Municipal Utility District (SMUD)

Adapted from the English Wikipedia article Loon Lake Dam, available under CC BY-SA 4.0Updated 7 August 2025

Loon Lake is a reservoir situated within the Eldorado National Forest in El Dorado County, California, United States. This reservoir was formed by the construction of Loon Lake Dam, finalized in as a component of the Upper American River Project managed by the Sacramento Municipal Utility District. The initiative is designed to capture spring snowmelt runoff, which is then utilized for hydroelectric power production during the summer and fall seasons. Loon Lake Dam holds back water at the source of Gerle Creek, which historically flowed intermittently through the natural basins of Loon and Pleasant Lakes. Currently, the majority of water entering Loon Lake is delivered through the Buck-Loon Tunnel from Buck Island Reservoir, located in the neighboring Rubicon River watershed. The area offers various recreational facilities including the Loon Lake Chalet for winter activities and summer amenities such as a boat launch and camping sites, although it experiences less visitor traffic compared to Union Valley Reservoir and the Rubicon Trail.

The reservoir is also referred to as Loon Lake Reservoir; boaters commonly identify its northeastern section as the Pleasant Lake Arm, which covers the submerged Pleasant Lake.

Development

The initial Loon Lake Dam was constructed in 1884 with the purpose of providing water during summer and fall months to Georgetown Ridge to support mining operations. The dam was owned by Georgetown Divide Water Co., which managed irrigation and canal systems extending from Gerle Creek to Georgetown Ridge. In 1943, E. F. Sullivan from the Bureau of Reclamation proposed harnessing Loon Lake for hydroelectric power generation. By 1948, the Georgetown Divide Public Utility District (GDPUD) applied for appropriative rights to divert up to 260,000 acre-feet of water from the American River basin via Loon Lake and Gerle Creek for irrigation, livestock watering, and domestic consumption.

Water Rights

The Georgetown Divide Public Utility District (GDPUD) originally held appropriative water rights granted by the State Water Resources Control Board alongside pre-1914 rights for diverting water from tributaries of Pilot Creek within the South Fork American River watershed. Early stakeholders in the Georgetown Divide Water Company included Sierra Pacific Power Company, Loon Lake Water and Power Company, California Water Company, and Pilot Creek Water Company; all asserted pre-1914 claims within the South Fork Rubicon and Pilot Creek drainage areas. These entitlements encompassed storage rights in Loon Lake as well as diversions from South Fork Rubicon River, Gerle Creek, Pilot Creek, and their tributaries. Water retained in Loon Lake was transported through a canal system connecting the South Fork Rubicon drainage to that of Pilot Creek.

In 1952, GDPUD took ownership of both water rights and operational control over infrastructure within the Georgetown service region from Georgetown Divide Water Company. This transfer included control over Loon Lake and water diversions from Rubicon and Onion Creek into Pilot Creek watersheds. During the period between 1940 and 1950, Sacramento Municipal Utility District (SMUD) pursued rights related to GDPUD facilities in the South Fork Rubicon watershed for its Upper American River Project (UARP). A formal agreement in 1961 transferred these rights—comprising pre-1914 water claims in the Upper Rubicon watershed and at Loon Lake—to SMUD. Following this transfer, SMUD filed applications for appropriative water rights associated with Loon Lake storage and diversions within the South Fork Rubicon basin extending into Silver Creek.

Hydroelectric Project

Between 1959 and 1985, SMUD developed the Upper American River Hydroelectric Project (UARP), initiating commercial operations in 1961. Encompassing roughly 674 square miles, the UARP watershed is characterized by rugged mountainous regions and deeply carved canyons. Mostly situated within Eldorado National Forest, the project includes eight generating stations and eleven reservoirs.

Loon Lake Facility

The Loon Lake Powerhouse is located more than 1,000 feet beneath Loon Lake and shares architectural features with the Helms Power Plant and Eastwood Powerhouse near Fresno, California. Water is released through an extended tunnel leading to Gerle Creek Reservoir. The electricity produced is transmitted via two 69-kilovolt lines mounted on common towers: one line connects Loon Lake to the Robbs Peak switchyard, while the other links it to the Union Valley switchyard.

Operation

SMUD primarily employs Loon Lake and its associated hydroelectric infrastructure for water storage purposes. Loon Lake, Ice House, and Union Valley Reservoirs collectively represent around 90% of the total storage capacity. Reservoir levels are raised in spring and summer to satisfy peak power demands and to facilitate whitewater recreational activities downstream during drier seasons. Water from Rubicon Reservoir and Buck Island Lake is channeled into Loon Lake through the Buck-Loon Tunnel. Throughout the year, water elevation in the reservoir fluctuates approximately 36 feet to balance ecological flow requirements, recreational use, and energy generation reliability.

CEQA

The 2014 California Water Quality Certification appendix details mitigation strategies addressing the ecological effects of Loon Lake on geology as well as aquatic and terrestrial habitats prior to dam construction in 1962. To accommodate increased recreational use stemming from the lake and its access roads, SMUD has invested in enhancements such as campground upgrades and a winter recreation chalet. Principal impacts include variable water levels, modified streamflows affecting aquatic ecosystems, visual landscape alterations, and elevated human pathogen levels associated with recreational activity.

Dams

The primary dam at Loon Lake is a rockfill embankment approximately 0.4 miles in length and 108 feet in height, featuring a 250-foot side channel spillway located on its right bank. Additional supporting structures include a rockfill Auxiliary Dam measuring 910 feet by 95 feet along the western shoreline and a smaller earthfill dike positioned on the northeast shore. Construction commenced in 1962 following removal of an earlier dam erected in 1872.

Water Quality

SMUD performs water quality monitoring at multiple depths quarterly—during initial major rainfall, spring runoff, summer low flow, and autumn turnover periods. In samples collected near the Loon Lake Tunnel-Buck Island outlet around 2000, temperatures ranged from 8°C to 21°C, with dissolved oxygen consistently between 8 and 9 mg/L, reflecting cold, clear water that is well oxygenated near full saturation. The reservoir maintains excellent water clarity with visibility reaching depths up to 36 feet.

Riparian Areas

Reservoirs within the Upper American River Project, including Loon Lake, support upland-type vegetation communities. Wetlands in this area are defined by steep gradients and well-drained soils, hosting species such as mixed conifers, firs, Huckleberry Oak, rocky shores, scattered wet meadows, and Lodgepole Pines. Two dominant wetland categories exist: lakeshore-basin meadows with seasonally inundated shorelines and depressional meadows found within swale formations. The largest wetland zone lies at the northern end of the reservoir, shaped by snowmelt and inflow patterns, encompassing approximately 38 acres.

Amenities

Camping

Situated along Highway 50 (Ice House Road), just south of Loon Lake and roughly 23 miles east of Placerville at an elevation of 6,500 feet, Loon Lake Campground operates from mid-July through mid-October. It features 53 campsites where visitors may stay up to 14 nights per year. Each individual campsite accommodates one vehicle and up to six occupants. Reservations can be secured through Recreation.gov.

Rubicon Trail

The Rubicon Trail offers a 22-mile route designed for four-wheel drive vehicles, including a designated off-highway vehicle section near the base of the Loon Lake Main Dam.

Fishing

The Department of Fish and Game stocks rainbow trout biweekly. Ice fishing is generally accessible from January until early March.

Boating

Boating is supported by a boat ramp adjacent to the campground and an informal launch site located on the northwest shoreline.

Hiking

Well-traveled hiking paths link Loon Lake Campground with Pleasant Campground, providing entry points into Desolation Wilderness.

Winter Recreation

During winter months, SMUD ensures that road access to Loon Lake Chalet and its parking area remains open.

External links