Seattle Port Lagoon No 3
Seattle Port Lagoon No 3 is an earth dam located in King County, Washington, built in 2001. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Seattle Port Lagoon No 3
The primary purpose of Seattle Port Lagoon No 3 is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Port Of Seattle (local government). It impounds the Des Moines Creek - Offstream.
The dam stands 32 feet tall and stretches 1,500 feet across, creates a reservoir covering 0 acres, and has a maximum storage capacity of 256 acre-feet. Completed in 2001, the structure is relatively new.
This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 05/03/2022.
At 32 feet, this dam is taller than 76% of dams nationwide.
Living Downstream
If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Washington dam safety program can provide more specific information about emergency planning for this structure.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Washington |
| County | King |
| River/Stream | Des Moines Creek - Offstream |
| Coordinates | 47.43254, -122.31332 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 32 ft |
| Dam Length | 1,500 ft |
| Year Completed | 2001 (25 years old) |
Storage & Hydraulics
| NID Storage | 256 acre-ft |
| Max Storage | 256 acre-ft |
| Normal Storage | 235 acre-ft |
| Surface Area | 0 acres |
| Max Discharge | 140 cfs |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | Port of Seattle |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 05/03/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | WA00671 |
| Federal ID | WA00671 |
| More Info | State Dam Safety Program |