Cowlitz River Project

Overview of the Cowlitz River Project

The Cowlitz River Project is Tacoma Power’s largest hydroelectric facility. It produces enough clean, renewable hydroelectric energy to serve more than 151,000 homes each year. This hydropower comes from the water stored behind the Mayfield and Mossyrock dams.

Built in 1963, Mayfield Dam forms 13-mile-long Mayfield Lake. Mossyrock Dam, built in 1968, is the tallest dam in Washington state at 606 feet above bedrock, and forms the 23.5-mile-long Riffe Lake. Watch a video detailing how we rebuilt the two Mossyrock powerhouse generators.

Cowlitz River Project map

Project Licensing

All four of our hydroelectric projects are licensed separately by the Federal Energy Regulatory Commission (FERC), which was created by the Federal Power Act to ensure safe and efficient operation of power plants across the U.S. Many other agencies, tribes, organizations and stakeholders are also an important part of the licensing process. In 2003, we received a 35-year federal license to operate the Cowlitz River Project.

Fish and Wildlife Programs and Public Recreation

Along with generating clean, renewable hydroelectric energy, our FERC license includes mandates for:

Tour the Facilities​

Free group tours of the Cowlitz River Project facilities are available by appointment for school, civic, business and recreational groups. To arrange a tour, please complete the request form at the bottom of our hydropower page.

Latest News

Would you like to receive updates about the Cowlitz River Project? Click here to sign up for our Cowlitz River Project email list.

Mossyrock Dam North Shore Fishing Trail is now open to the public.

The Cowlitz Restoration and Recovery 2024 grant funding round is now open. Learn more about the program here.

Tacoma Power to lower Cowlitz River flows below Mayfield Dam to 2,360 cfs starting July 1. Learn more about the reduction here.

Updates as of April 2023:

Why is Riffe Lake so low?
The Riffe Lake boat launches are unavailable due to an ongoing extreme lack of precipitation, which began in 2022. Following a dry October and November, much of the precipitation we have received has been in the form of snow. That snowpack won’t help refill Riffe Lake until the temperatures warm up enough for it to melt. This lack of available water means very low inflows into Riffe Lake. Click here to learn more.

Riffe Lake recreational access update
Public safety is a top priority for Tacoma Power, so we reduced the maximum level of Riffe Lake from 778.5 to 749 feet in 2017 due to updated seismic loading concerns for the Mossyrock Dam spillway piers (not the dam itself).

Lowering the maximum lake elevation impacted recreational access, so, in 2018, we invested approximately $850,000 into improvements at Mossyrock Park. We extended one boat launch ramp (it was usable to 737 feet and is now usable to about 708 feet; the other ramp is usable to about 724 feet) and built a new swim area and ADA facilities, including an ADA-accessible parking lot, trail to the swim area, and restroom.

More recently, we discussed potential improvements on the east end of the lake with local elected officials and the public. After an extensive vetting process, we chose two projects that will improve the use and safety of the Taidnapam North boat launch. Read about them here.

Mossyrock Dam seismicity studies update
Revised seismic hazard data from the United States Geological Survey indicated that the Mossyrock Dam spillway piers and gates (not the dam itself) could potentially be damaged in the event of a large earthquake. If the gate structures are damaged when the lake is at a full level, this could cause an extreme downstream flooding event. Although the earthquake probability is very low, we decided to reduce this risk by keeping Riffe Lake’s elevation to about 30 feet lower than full (778.5 feet). The drawdown began in 2017. We worked with our regulators to make this decision, and they approved our plan to voluntarily lower the level.

Our objective is to bring Riffe Lake back to full pool. We are working hard to make progress on identifying potential seismic damage to any other parts of the dam, as well as possible seismic retrofits, but this is a long and complex process. Read more about our progress here.

Satellite fish rearing facilities update
We will build three satellite fish rearing facilities as indicated in our federal license. With the partnership of the Cowlitz Fisheries Technical Committee, Tacoma Power has evaluated many potential satellite rearing facility locations and programs. We have worked for years on this project and are excited to have selected our first site; it is in the upper Cowlitz basin and is owned by Energy Northwest. The Energy Northwest location offers multiple benefits, including a cool and stable water supply, good site security, and excellent access. Read more about our selection process here. We look forward to your feedback on the proposed Energy Northwest location and would also like to know if you have ideas for locations of the other two future facilities. Please send your comments to Cowlitz Fish Facilities manager Eric Shoblom at

Sign up for Lewis County Emergency Management alerts
We conducted our annual emergency siren testing at Ike Kinswa State Park, Mayfield Lake Park, and the Cowlitz Salmon Hatchery on April 5. We perform the test on the first Wednesday of each April. Lewis County Emergency Management sends alerts before and after the test. Get ready for next year by signing up for alerts online here.

Check out our fish game for kids!
We’re big fans of fish at Tacoma Power! Kids can learn about which species we raise by printing and filling out this page! Scroll down to the bottom of this section for the answers…

2023 grant round for Cowlitz Hatchery-Associated Production projects: Second workshop opportunity
Do you have ideas for how to help protect and promote restoration and recovery of upper Cowlitz River basin salmonids (spring/fall Chinook, coho and winter steelhead)? Consider applying for a 2023 Hatchery-Associated Production (HAP) project grant through our Cowlitz Restoration and Recovery (CRR) Program. Hatchery-Associated Production projects include the artificial production or rearing of fish to support recovery of the CRR Program target species and populations. Conservation non-profits, Native American Tribes, regional fisheries enhancement groups, conservation districts, local and state governmental entities, and federal agencies are eligible and encouraged to apply. The funding process runs through late fall of 2023.

Learn more by visiting our HAP webpage.

Questions? Contact Tacoma Power CRR Program staff contact Melora Shelton at or 253.441.4994.

Kosmos Flats Oil Seep Capped
As part of our commitment to ensuring good stewardship of our environment, Tacoma Power capped the Kosmos Flats oil seep in December 2019. Read more about the project.

Fish game answers!

  1. Sockeye
  2. Coho
  3. Chinook
  4. Steelhead
  5. Cutthroat Trout

At our Cowlitz River Project in Lewis County, we raise and release spring Chinook, fall Chinook, coho, summer-run steelhead, winter-run steelhead, and sea-run cutthroat trout. Learn more about our Cowlitz fisheries programs and check out our Cowlitz Fish Report for weekly updates.

At our Cushman Hydro Project in Mason County, we raise and release spring Chinook, winter-run steelhead, coho, and sockeye. Learn more about our Cushman fisheries program.

Public Meetings

Cowlitz Fisheries Science Conference and Annual Program Review Hybrid Meeting – Aug. 22, 2023
In person at the Veterans Memorial Museum (100 SW Veterans Way, Chehalis, 98532)/Microsoft Teams
10 a.m. to 4 p.m.
38 in-person attendees; 26 online attendees

Hosted by Tacoma Power and the Washington Department of Fish and Wildlife.



Cowlitz Annual Program Review Virtual Public Meeting – June 1, 2022
Online/conference call | 2 to 3 p.m.
26 attendees

Hosted by Tacoma Power and the Washington Department of Fish and Wildlife.

Cowlitz Annual Program Review and Science Conference – April 21, 2022
Online/conference call | 8 a.m. to 4 p.m.
44 attendees


Cowlitz Fisheries and Hatchery Management Plan (FHMP) Transition Plans Virtual Public Meeting – Feb. 22, 2022
Online/conference call | 3 to 5 p.m.
32 attendees

Cowlitz Annual Program Review Virtual Public Meeting – June 23, 2021
Online/conference call | 2 to 4 p.m.
14 attendees

Cowlitz Annual Program Review and Science Conference – May 19, 2021
Online/conference call | 10 a.m. to 4 p.m.
37 attendees


Summarize Five-Year Trends

  1. Introduction and Meeting Logistics
  2. Intro to Current Status
  3. Project Operations
  4. Hatchery Operations
  5. Habitat
  6. Passage
  7. Pre-Terminal/Terminal Harvest
  8. SARs
  9. Lower Cowlitz Adult Estimates
  10. Separator Returns
  11. What We Know/Don’t Know in Our Current State

Annual Program Review

  1. Summary of Recent Trends and Current Status, Fisheries and Hatchery Management Plan – Transition Plans Status and Next Steps, 2022 Strategies

Please email with questions.

Cowlitz River Fisheries and Hatchery Management Plan (FHMP) and Annual Project Review (APR) Virtual Public Meeting – Aug. 12, 2020
Online/conference call | 4 to 6 p.m.
21 attendees

Cowlitz River Annual Project Review (APR) Public Meeting – Aug. 14, 2019
Veterans Memorial Museum | 6 to 8 p.m.

Cowlitz River Annual Project Review and Fisheries Science Conference – July 10, 2019
Veterans Memorial Museum | 9 a.m. to 3 p.m.
51 attendees