Beaver Lake Restoration Approaches - Phase 2

Beaver Lake and Mompano Dam are located within the 21,573-acre Abernethy Creek watershed. The creek is a tributary of the Willamette River entering near Oregon City, below Willamette Falls. The Greater Oregon City Watershed Council has been working with the Beaver Lake Homeowners Association and various community stakeholders since 2021 to advance understanding of the lake, dam, fish ladder and associated risks and challenges. Modification of the existing fish ladder is needed to ensure native migratory fish have access to over 8 miles of high-quality spawning and rearing habitat upstream of the dam. Water quality issues at the lake have been identified including shallowing due to sedimentation, seasonal temperature increases, harmful algal growth, and nutrification. In the first phase of the project, a steering committee was formed made up of stakeholder representatives, watershed council members and staff, and technical expertise. The steering committee developed and presented background on the project for the HOA board which was well received. Subsequent to the presentation, additional work was identified to more effectively scope the challenges associated with the dam and develop a suite of proposed alternatives for consideration. Building relationships with the HOA board and lake committee has progressed more slowly than expected. However, recent meetings with the ODFW fish passage team and a US Fish & Wildlife Service lamprey passage expert have advanced the interest of the HOA in working collaboratively to fully understand and address the immediate needs for repair while also considering long-term solutions.

This Phase 2 proposal seeks additional funding and time to implement the recommended actions identified by the steering committee for planning assistance. Phase 2 will build on this framework to work with the community and interested parties to identify “desired conditions” for Beaver Lake and Abernethy Creek and provide ranked alternatives.

The goal of the Beaver Lake Restoration Approaches to Abernethy Creek - Phase 2 remains to develop and
refine multiple concepts to improve fish passage, water quality, and riparian and instream habitat within, above, and
below the Beaver Lake/Mompano dam focal area. Concepts will be shared with stakeholders and technical experts
for refinement and to develop consensus. Selected concepts will be proposed for design and implementation to
improve habitat for native fish in Abernethy Creek.
The Abernethy Creek watershed is essentially split in two with the Beaver Lake/ Mompano Dam site creating a
significant difference in the quality of water and habitat upstream and downstream of the dam. The 58-acre Beaver
Lake is a man-made impoundment constructed in the early 1970’s for fish culture and recreation by a private
developer. Surrounding the lake, 80 private lots comprise a 470-acre development that is known as Beaver Lake
Estates.
The dam and associated fish ladder impedes passage of native migratory fish into higher quality habitat upstream
and the lake impacts water quality downstream by increasing water temperature and reducing dissolved oxygen. As
a result, the vast majority of spawning by Pacific lamprey, coho, and winter steelhead is downstream of the dam
where adult fish are restricted to lower quality spawning habitat and juvenile fish are restricted to rearing habitat
impacted by high summer water temperature.
The primary audience for engagement through this project is the Beaver Lake Homeowners Association, a group of
landowners with a common interest in the management and care of the reservoir and waterways to maintain the
values and investment in their properties. Additionally, property owners immediately below the dam along
Abernethy Creek including Clackamas County are anticipated to be important participants in the project. Finally,
upstream of Beaver Lake, several larger scale landowners such as the Port Blakely timber company will be
contacted to assess interest in participation.
Engagement with these various stakeholders at this juncture in time is critical as the native fish populations in
Abernethy creek including coho, steelhead, and lamprey are facing increasing pressure from climate-induced
impacts such as extreme temperature events and intense storm runoff leading to potentially lethal water quality
impairments. At this time, an opportunity exists to bring together technical expertise with property owners in a
facilitated process which will develop specific project concepts for habitat restoration in the focal area. Due to the
complex nature of the fish passage issues and the water quality impacts presented by the reservoir, an expanded
scope which considers habitat restoration immediately downstream and upstream of the reservoir is proposed. This
scale is appropriate given the high-level impacts to Abernethy Creek presented by the current conditions.
Cool water refuge is present in tributaries of the watershed downstream of the dam, but it is limited and currently
not capable of increasing rearing capacity significantly due to habitat limitations in those tributaries. The OWEB
funded restoration project Holcomb Creek #1 was completed in 2023 to restore a lower watershed tributary that is
capable of providing cool-water refuge for fish moving out of Abernethy Creek in summer months. This project will
increase rearing capacity in a cool water tributary, but without significant investment in restoration of the riparian
corridor, stream temperatures will likely increase in the future and limit rearing potential.
Climate change impacts are likely to further limit spawning and rearing potential in the lower portions of watersheds
already impacted by excessive stream temperatures that can be lethal to salmonids and lampreys.