Moccasin Lake Dam
Moccasin Lake Dam is an earth dam located in Okanogan County, Washington, built in 1969. It carries a High hazard potential classification and has a fair condition assessment.
About Moccasin Lake Dam
The primary purpose of Moccasin Lake Dam is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by Moccasin Lake Ranch #1 Inc. (private). It impounds the Tr-thompson Creek-offstream near Twisp.
The dam stands 17 feet tall and stretches 530 feet across, creates a reservoir covering 27 acres, has a maximum storage capacity of 261 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1969, the structure is well into its service life at over 50 years old.
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 fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 08/20/2019.
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 | Okanogan |
| Nearest City | Twisp |
| River/Stream | Tr-thompson Creek-offstream |
| Coordinates | 48.42145, -120.20559 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 17 ft |
| Dam Length | 530 ft |
| Year Completed | 1969 (57 years old) |
Storage & Hydraulics
| NID Storage | 261 acre-ft |
| Max Storage | 261 acre-ft |
| Surface Area | 27 acres |
| Drainage Area | 0 sq mi |
| Max Discharge | 35 cfs |
Ownership & Safety
| Purpose | Irrigation |
| Owner | Moccasin Lake Ranch #1 Inc. |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 08/20/2019 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | WA00053 |
| Federal ID | WA00053 |
| More Info | State Dam Safety Program |