The Skagit River Hydroelectric Project (Project) is located in the upper Skagit River basin, in northeastern Puget Sound, Washington.  Headwaters of the Skagit River originate in Canada, and the Project occupies a scenic area in the Mount Baker-Snoqualmie National Forest and Ross Lake National Recreation Area, adjacent to North Cascades National Park.  The Skagit River basin, the third largest in Washington, drains 3,140 square miles, including about 390 square miles in Canada.  The Skagit River and its tributaries drain mountain areas from east to west, entering the United States from British Columbia at river mile (RM) 127 and flowing a total of 162 river miles to Puget Sound near Mount Vernon, Washington (Envirosphere 1988).  The basin is characterized by rugged mountain topography in the central and eastern parts, and by level floodplains and rolling uplands in the western part.

The three Project dams, Ross, Diablo, and Gorge, are located at RMs 105, 101, and 97, respectively.  Combined they have a total power generating capacity of about 690 MW, as reported to FERC.  Project hydropower development by Seattle City Light (SCL) spanned three decades, with the completion of Gorge Dam in 1924, Diablo Dam in 1936, and Ross Dam in 1952.

Project Name Skagit
LIHI Certificate Number 5
LIHI Effective and
Expiration Dates
May 15, 2008
May 15, 2016
(extended to July 31, 2017)
Owner Seattle City Light
State Washington
Location Located in the upper Skagit River Basin, in northeastern Puget Sound, Washington.
Installed Capacity Total: 689.94 MW
Gorge Powerhouse: 207.48 MW
Diablo Powerhouse: 122.46 MW
Ross Powerhouse: 360 MW
Average Annual Generation 2,414,772 MWh
Facility Type
FERC No. 553

In 1991, SCL entered into historic Settlement Agreements with twelve stakeholders as part of Project relicensing.  The stakeholders included federal and state agencies, Native American Tribes, and an environmental group. These agreements were submitted as a package to the Federal Energy Regulatory Commission (FERC) and were intended to fully mitigate the Project’s environmental impacts, a key element in license renewal (FERC 1991).  For large hydro projects such as the Skagit, the environmental mitigation package historically has been determined by the FERC.  SCL’s goal was to reach agreement, through a collaborative process with the stakeholders, on environmental mitigation and a new license.  Settlement Agreements on fisheries, wildlife, recreation and aesthetics, erosion control, cultural resources (archaeological and historic resources), and traditional cultural properties were signed by all parties.

The Agreements were recognized as a national model and have been called “the most comprehensive set of Settlement Agreements for the public good ever submitted to FERC.”  (Dean Shumway, Director, FERC Office of Hydropower Licensing, December 18, 1992).  On May 16, 1995, the FERC issued a new operating license that largely incorporates the Settlement Agreements as license requirements.  An order on rehearing, issued on June 26, 1996, incorporates the remainder of the Settlement Agreements into the license.

The three dams are hydraulically coordinated to supply approximately one-fourth of SCL’s power requirements, while maintaining instream flows beneficial to salmon reproduction and rearing.  In addition, the Project provides flood control storage and a variety of high-quality recreational opportunities, including hiking, sport fishing, boating, and guided tours.  The fish resources and the area’s scenic qualities were integral in the lives of Native American tribes who occupied the basin.  Many historic cultural sites can be found throughout the basin.

Ross Dam, the Project’s uppermost facility, impounds the high-quality waters of Ross Lake, a 24-mile-long reservoir extending about 1½ miles north of the U.S.-Canada border.  Ross Lake, which is surrounded by the Ross Lake National Recreation Area, is the primary storage reservoir for the Project; it is used for flood control as well as power generation.

Water level fluctuations in Ross Lake vary annually and may range from 1,602.5 feet above mean sea level (MSL) to 1,475 ft MSL.  SCL maintains the reservoir near full-pool elevations from July through October for recreational and aesthetic purposes.  Reservoir elevations remain high through the migratory and spawning periods of native char (bull trout and Dolly Varden) and rainbow trout, allowing these species access from the lake to high-quality spawning grounds in the tributaries.  Lands bordering Ross Lake are moderately to steeply sloped and forested; glaciers draining to the basin contribute cool waters that provide excellent summer habitat for native bull trout and rainbow trout.  Major tributaries to Ross Lake include Big Beaver, Little Beaver, Ruby, Lightning, and Devil’s creeks (Envirosphere 1988).

Diablo Dam, located downstream from Ross Dam creates Diablo Lake which is 4½ miles long and used primarily for daily and weekly regulation of discharge from Ross.  Full pool elevation is 1,205 ft MSL and annual water level fluctuations range from 10 to 12 ft.  Much of the land surrounding Diablo Dam consists of steep, exposed rock or talus sparsely covered with scattered conifers and shrubs.  The remaining areas are moderately to steeply sloped and forested.  Thunder Creek is the major tributary to Diablo Lake (Envirosphere 1988).

The most downstream generating facility, the Gorge Dam and Powerhouse, is located about 4 miles downstream of Diablo Dam.  Gorge Lake is smallest of the three Skagit reservoirs and fluctuates only a few feet from its full pool elevation of 875 ft MSL.  Both the Diablo and Gorge facilities are operated with water released from Ross Powerhouse.  There is very limited storage in the Gorge and Diablo reservoirs.  Gorge Lake is aptly named for the cliffs and talus slopes comprising much of the area bordering the reservoir.  The few flat areas adjacent to the reservoir are developed, and the remaining steep areas have been logged (Envirosphere 1988).

The Gorge reach of the Project marks the historical limit of anadromous salmon migrations in the upper river.  Below the Gorge Powerhouse, the river is free of impoundments and is protected under the National Wild and Scenic Rivers Act.  River reaches immediately downstream of the Powerhouse are most affected by Project operations.  Project influences on river flows decrease progressively downstream, and are moderated by flow contributions from major tributaries that include the Cascade (RM 77), Sauk (RM 66), and Baker (RM 56) rivers.


Certification History

December 16, 2016: The Skagit Hydroelectric project has been granted an additional extension of the current certificate term. The new expiration date is July 31, 2017. See extension letter for explanation below.

March 18, 2016: The Skagit Hydroelectric project has been granted an extension of the current certificate term. The new expiration date is November 15, 2016. See below for extension letter.

August 28, 2008: The Skagit River Project has been recertified as low impact, continuing to meet LIHI’s eight environmentally rigorous criteria. The project was issued an eight-year certificate, effective May 15, 2008 and expiring May 15, 2016.

July 12, 2008: The Low Impact Hydropower Institute received a comment letter from Aaron Johnson regarding the certification of the Skagit Hydroelectric Project. The letter can be found in the Files section below.