Mossyrock
Cowlitz River·
Lewis, Washington·
Built 1968·
Arch·
366 ft tall
Physical Details
| Dam Height | 366 ft (taller than 94.6% in WA) |
| Dam Length | 1,750 ft |
| Dam Type | Arch |
| Max Storage | 1.9M acre-ft |
| Normal Storage | 1.7M acre-ft |
| Drainage Area | 1,042 sq mi |
| Max Discharge | 280,000 cfs |
| Year Completed | 1968 (58 years old) |
| NID ID | WA00151 |
Safety Information
High Hazard
Loss of human life is likely if the dam fails
Emergency Action Plan: Yes
Last Inspection: June 28, 2022
State Regulated: No
Ownership
City of Tacoma
Public Utility
Nearby Dams
Frequently Asked Questions
What is the hazard classification of Mossyrock?
Mossyrock is classified as High Hazard. Loss of human life is likely if the dam fails.
Who owns Mossyrock?
Mossyrock is owned by City of Tacoma (Public Utility).
When was Mossyrock last inspected?
Mossyrock was last inspected on June 28, 2022.
When was Mossyrock built?
Mossyrock was completed in 1968, making it 58 years old.
Data from the National Inventory of Dams (NID) maintained by the US Army Corps of Engineers. Dam conditions may have changed since the last update. This site is not affiliated with USACE. Do not use for emergency planning — contact your local dam safety program.