Fern Ridge project data

Dam length 6,330 ft 1,929.3 m
Height 44 ft 13.4 m
Elevation (NGVD*) 379.5 ft 115.7 m
Lake length 4.5 mi 7.2 km
Area when full 9,000 ac 3,688.5 ha
*National Geodetic Vertical Datum

Contact us about Fern Ridge:
General: 541-684-4300
Recreation: 541-942-5631

Email us about Fern Ridge

Fern Ridge pamphlet

Comment on the Long Tom River drop structure modification:

The public can also submit comments via e-mail, written correspondence or electronically (GIS):
Mail: U.S. Army Corps of Engineers, CENWP-PM
ATTN: Kat Herzog or Sarah Knowles
P.O. Box 2946
Portland, OR 97208-2946

Fern Ridge Dam & Reservoir

Fern Ridge Dam is at river mile 23.6 on the Long Tom River, a tributary of the Willamette River, about 12 miles west of Eugene, Ore. Fern Ridge is an earthfill structure with a gated concrete spillway and outlet works for regulating lake levels, which was completed in 1941 at a cost of $6 million. Since then, it has prevented more than $415 million in potential flood damages. The reservoir provides 110,000 acre-feet of usable flood control storage and controls runoff from a 275 square-mile drainage area.

Fern Ridge Dam was the first Willamette Valley dam constructed by the U.S. Army Corps of Engineers. Its authorized purposes are flood risk management, water quality improvement, irrigation, fish and wildlife habitat and recreation.

Long Tom River

Project Description
Fern Ridge Dam is located on the Long Tom River 13 miles upstream of Monroe, Ore., and 24 miles upstream of the confluence of the Long Tom and Willamette Rivers. Fern Ridge Dam is a 50-foot tall, 6,330-foot long earthen embankment dam built on a soil foundation with a concrete spillway, six spillway gates, a gated regulating outlet, and two earthen auxiliary dikes. Fern Ridge Dam is owned, operated, and maintained by the Portland District of the U.S. Army Corps of Engineers (USACE). Construction of the dam began in 1940 and was completed in 1942. In 2005, the downstream portions of the earthen embankment were completely reconstructed to address concerns with seepage through the embankment’s soil foundation. The reconstruction included installation of a drainage system to collect seepage through the foundation and instrumentation to monitor the drainage system's performance during normal reservoir operations and during flood events. Fern Ridge Dam is part of a system of 13 multi-purpose dams in the Willamette Valley with the primary purpose of flood risk management and secondary purposes of recreation, irrigation, municipal and industrial water supply, fish and wildlife,  water quality and hydropower. Collectively, this system of dams is referred to as the Willamette Valley Project (WVP.) Fern Ridge is one of four WVP dams that do not include a powerhouse.   

During the winter months, the Willamette Valley Project reservoirs are maintained at their lowest elevations to allow for the temporary storage of rain and snow melt. When managing high flow events, the outflow from the system of dams is coordinated to reduce peak flows and river stages at downstream locations. In spring, USACE begins to fill the reservoirs, increasing the amount stored for conservation purposes and reducing the amount available for flood risk management.  During summer, stored water is used for recreation on the reservoirs, and some stored water is released in the river downstream to improve water quality, support fish and wildlife habitat, and provide water for irrigation and municipal uses. During dry summer months, flows into the reservoirs are generally less than flows needed to meet minimum flow objectives, causing reservoir levels to drop. In fall, stored water remaining in the reservoir is drawn down to minimum levels in preparation for the flood season.  

Fern Ridge Dam is located about 50 miles east of the Cascadia Subduction Zone, a megathrust fault along the Oregon Coast. The Cascadia Subduction Zone is capable of producing very large, long duration earthquakes. The last Cascadia Subduction Zone earthquake occurred in the year 1700. 

Risk Characterization: Moderate
USACE performed a routine risk assessment for Fern Ridge Dam in 2020 that characterizes the risk associated with the dam to be Moderate. USACE performs risk assessments as part of an ongoing dam safety program and to assist in the prioritization of investment for aging infrastructure.  The risk assessments evaluate the life safety risks associated with the dams to determine if risk reduction actions are needed and, if so, what actions should be taken.  

The assessment considers a wide range of hazard scenarios from the most likely to the most extreme and unlikely.  The risk at Fern Ridge Dam is driven primarily by the potential for an earthquake occurring at the same time reservoir elevations are the highest.  The Cascadia Subduction Zone fault can produce very large earthquakes that can cause up to three to five minutes of ground shaking. The last subduction zone earthquake occurred in 1700. Fern Ridge Dam has never experienced a large earthquake, but because of its proximity to the Cascadia Subduction Zone and its soil foundation, the earthen embankment dam at Fern Ridge Dam is expected to experience stronger shaking from a Cascadia Subduction Zone earthquake than the other Willamette Valley Projects.  It is difficult to predict the exact amount of damage or settlement that could occur to a dam as a result such an earthquake. A large earthquake could cause the earthen dam to settle, resulting in water overtopping the dam. The speed and depth of water overtopping a damaged dam could erode the soil that forms the dam and cause flooding downstream.  The shaking from an earthquake could also open up cracks through the earthen embankment, allowing water to flow through the dam.  The force and speed of the flowing water through a crack in the earthen embankment could cause the dam to be further damaged by eroding away the embankment material, resulting in uncontrolled release of water from the reservoir, and flooding areas downstream. The flooding would be most severe in the agricultural lands between the dam and the confluence with the Willamette River, between Monroe and Corvallis, Oregon. 

USACE is confident that the Willamette Valley dams are well-built, well-maintained, and will continue to significantly reduce flood risks for the region. However, the dams cannot eliminate potential for flooding. Even with the presence of the Willamette Valley dams, extreme rainfall and snowmelt events may result in flooding in areas downstream of dams.  Flooding can be caused by high flows resulting from unregulated portions of the watershed and/or high flow that must be passed through the dam outlets and spillways when reservoir storage capacities are exceeded.  

Risk Management Measures
USACE is further addressing the risk at Fern Ridge Dam by pursuing an advanced risk assessment of the earthen embankment's response to earthquake shaking so that potential damages are better understood. This will help inform the likelihood of an uncontrolled release of water following an earthquake and whether there is a need to pursue long-term risk reduction measures. USACE regularly conducts routine inspections of its dams and Fern Ridge Dam is equipped with instrumentation to monitor dam performance and seismic activity. Post-earthquake procedures are in place to inspect and evaluate earthquake damages and USACE conducts routine dam safety exercises with local Emergency Managers and first responders. Fern Ridge Dam’s Emergency Action Plan (EAP) outlines actions to be taken during an emergency. USACE will update the EAP based on recent risk assessment results and information from updated inundation maps. In addition, USACE will continue and increase its outreach to improve community awareness of flood risks and risks associated with the dam.  

Long Tom River drop structure at Monroe

The City of Monroe identified a Corps-constructed drop structure as a fish passage barrier and the historic channelization of the Long Tom River as a factor in the disconnection of nearby side channels in a letter of interest on August 8, 2016. The Long Tom River is a priority watershed within the Willamette River system because of its potential high-quality juvenile salmon rearing habitat, as well as spawning and rearing habitat for cutthroat trout, lamprey and other native species. 

The Confederated Tribes of Siletz Indians (CTSI) submitted a signed letter on August 31, 2020 stating approval by Tribal Council of their co-sponsorship with the City of Monroe for a project to study the removal of this drop structure. 

The Long Tom Watershed Council (non-governmental organization) is a partner to the Sponsors on the project. 

The project has two goals and a number of objectives.

Goal 1: Restore Quality Habitat for Native Fish and Wildlife Species.

  • Objective: Improve year-round aquatic habitat diversity associated with in-stream features, for native fish use of spawning, rearing, and overwintering.
  • Objective: Reconnect and restore the historic disconnected channel segments to promote a more natural hydrologic regime.
  • Objective: Restore adjacent riparian and wetland habitat.

Goal 2: Restore and Emulate Natural River Processes, Structures, and Functions to Improve Fish Passage and Maintain Channel Conveyance.

  • Objective: Improve fish passage at Monroe’s drop structure.
  • Objective: Maintain channel conveyance
  • Objective: Restore side and main channels’ hydrodynamic, sediment transport, and geomorphic processes to sustain long-term fish passage.

The Corps and its partners held and recorded a virtual public information session, November 3rd, 2021 from 4-5 p.m. You can view it here. The slides are available here.

Fern Ridge recreation

Boaters: Click here to view Fern Ridge's water surface elevation map.

Birding: The Fern Ridge area is an excellent location for birding. Oregon’s largest breeding colony of purple martins can be found at Fern Ridge. Thousands of acres of emergent marsh support summer breeding habitat for a variety of water-bird species. Read more about purple martins: Corps reservoirs benefit Willamette Valley Swallows.

Day-use parks: Three day-use sites at Fern Ridge are privately operated: Eugene Yacht Club https://www.eugeneyachtclub.org/ or call 541-357-6860), Fern Ridge Shores (or call 541-935-2335) and Tri-Pass Ski Club (https://tripassskiclub.com/ or call 541-935-1495).

Kirk Park is located below Fern Ridge Dam off Clear Lake Road and gives access to the Long Tom River and ponds full of fish and wildlife. There are no group picnic areas or shelters available for reservations. Kirk Park has trails, picnic tables, paved roads, fire rings and vault toilets. Kirk Park is open dawn to dusk, mid-May to early September. Shore Lane Park is located at the end of Shore Lane Road on the northeast shore-line of Fern Ridge Lake.  This small, rustic park has a vault toilet and it is often used for launching paddle craft.  Shore Lane Park is open dawn to dusk, mid-May to early September. Jeans Park is located on Jeans Road on the west side of Fern Ridge Lake near Veneta. This wooded park has trails, vault toilets and limited parking. It is open year-round. For more information about the above parks, call the Willamette Valley Project Park Ranger Office at 541-942-5631.

Four day-use sites at Fern Ridge are operated by Lane County Parks: Orchard Point Park, Perkins Peninsula Park, Richardson Park and Zumwalt ParkCall Lane County Parks at 541-682-2000 or visit their website. Richardson Park also has a life jacket loaner station available.

Three day-use sites at Fern Ridge are privately operated. Fern Ridge Shores (or call 541-935-2335) and Tri-Pass Ski Club (541-935-1495).


Getting around

Environmental stewardship at Fern Ridge Dam

The Fern Ridge Project encompasses more than 11,000 acres, ranging from open water to marsh, wet prairie and upland prairie habitats. More than 5,000 acres of the Fern Ridge Wildlife Area is managed cooperatively with the Oregon Department of Fish and Wildlife. In addition, the Corps works with the Oregon Department of Fish and Wildlife to support resident game and non-game fisheries within the Long Tom River Basin.

The Willamette Valley Environmental Stewardship program focuses on restoring degraded uplands, wetlands and streams on Corps lands. Recent efforts include replacing exotic and invasive plants with native trees and shrubs, and restoring hydrology and topography to support native plant communities and wildlife habitat. The upland prairies and extensive wetlands at Fern Ridge provide habitats for a variety of plants and animals. Fender’s blue butterfly and its host plant, Kinkaid’s lupine, occupy upland prairie habitat around the lake.

Oregon’s largest breeding colony of purple martins is at Fern Ridge, as well as significant populations of breeding western pond turtles. Thousands of acres of emergent marsh support the summer breeding habitat for a variety of water-bird species.

Native upland prairies, along with wet prairies, now cover much less than one percent of their former area, making them some of the rarest North American ecosystems. Remnants of these highly diverse, complex and poorly understood ecosystems provide necessary habitat for many rare species. More than 50 rare species can be found at Fern Ridge, including several species federally listed as threatened or endangered.

The Fern Ridge Lake Shoreline Management Plan was developed in 1988 and revised by Addendum in 1997. Also, view these related materials: Moorage Guidelines.


Public Comment Period Open for Long Tom Channel Improvement Project

The Corps is proposing modifications to the Long Tom Channel Improvement Project in Benton County, OR. The draft Integrated Feasibility Report and EA is available for download  at:  https://usace.contentdm.oclc.org/utils/getfile/collection/p16021coll7/id/23788
Appendix C: Climate change assessment: Library Link
Appendix D: Economic and incremental cost analysis: Library Link
Appendix E: Habitat evaluation, benefits, quantification, and incremental analysis: Library Link
Appendix H: Engineering and design: Library Link 
​Appendix I: Hydraulics and hydrology: Library Link