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

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

Tacoma Power and the Washington Department of Fish and Wildlife cordially invite you to a Cowlitz Annual Program Review public meeting on Wednesday, June 1, from 2 to 3 p.m. The meeting will be hosted virtually via Microsoft Teams. Check out the agenda.

You do not need to RSVP.

Click here to join the meeting

 Or call in (audio only)
+1 253-666-4424
Phone Conference ID: 151 314 598#

Please email with questions.

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

The FHMP transition plans outline how we will organize and guide the Cowlitz fisheries/hatcheries programs. They are in final draft form, and we would like to hear your thoughts about them.

We will receive public feedback at the meeting, and will also receive written feedback until 4 p.m. PST on Feb. 25, 2022. Please send your feedback to

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

Please email with questions.

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