Polson Sewage Lagoon is an earth dam located in Lake County, Montana, built in 1963. It carries a Significant hazard potential classification.
Dam profile
NID height · 8 ft8 ft tall and 3,200 ft long. Height is drawn to scale against a two-story house, about 25 ft; the profile is a generic embankment section and the water level is illustrative.
About Polson Sewage Lagoon
Polson Sewage Lagoon is a dam in Lake, Montana. The dam is owned by City of Polson (local government). It impounds the Tr-flathead River near Agency.
The dam stands 8 feet tall and stretches 3,200 feet across, and has a maximum storage capacity of 84 acre-feet. Completed in 1963, 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.
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Location
| State | Montana |
| County | Lake |
| Nearest City | Agency |
| River/Stream | Tr-flathead River |
| Coordinates | 47.68650, -114.17820 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 8 ft |
| Dam Height | 8 ft |
| Dam Length | 3,200 ft |
| Year Completed | 1963 (63 years old) |
Storage & Hydraulics
| NID Storage | 84 acre-ft |
| Max Storage | 84 acre-ft |
| Normal Storage | 84 acre-ft |
Ownership & Safety
| Purpose | Other |
| Owner | City of Polson |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | MT01422 |
| Federal ID | MT01422 |
| More Info | State Dam Safety Program |