Greybull Sewage Treatment Lagoon
Greybull Sewage Treatment Lagoon is an earth dam located in Big Horn County, Wyoming, built in 1960. It carries a Significant hazard potential classification and has a fair condition assessment.
About Greybull Sewage Treatment Lagoon
Greybull Sewage Treatment Lagoon is a dam in Big Horn, Wyoming. The dam is owned by Town Of Greybull (local government). It impounds the Offstream near Greybull.
The dam stands 8 feet tall and stretches 4,800 feet across, creates a reservoir covering 31 acres, and has a storage capacity of 152 acre-feet. Completed in 1960, the structure is well into its service life at over 50 years old.
This dam has a significant hazard potential classification, meaning that a failure could cause significant economic damage — flooding roads, bridges, or property downstream — but is not expected to result in loss of life. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. The most recent inspection on record was 04/15/2025.
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Location
| State | Wyoming |
| County | Big Horn |
| Nearest City | Greybull |
| River/Stream | Offstream |
| Coordinates | 44.51250, -108.06270 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 8 ft |
| Dam Height | 8 ft |
| Dam Length | 4,800 ft |
| Year Completed | 1960 (66 years old) |
Storage & Hydraulics
| NID Storage | 152 acre-ft |
| Normal Storage | 152 acre-ft |
| Surface Area | 31 acres |
| Spillway Type | None |
Ownership & Safety
| Purpose | Other |
| Owner | TOWN OF GREYBULL |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Fair |
| Last Inspection | 04/15/2025 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | WY02058 |
| Federal ID | WY02058 |
| More Info | State Dam Safety Program |