Big Lake is an earth dam located in Missoula County, Montana, built in 1915. It carries a Significant hazard potential classification.
Dam profile
NID height · 30 ft30 ft tall and 440 ft long, taller than 68% of U.S. dams with a recorded height. 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 Big Lake
The primary purpose of Big Lake is water supply. The dam stores water for municipal, industrial, or agricultural use, helping ensure a reliable supply for the surrounding area. The dam is owned by City of Missoula (local government). It impounds the Tr-lake Creek near Missoula.
The dam stands 30 feet tall and stretches 440 feet across, creates a reservoir covering 38 acres, has a maximum storage capacity of 621 acre-feet, and collects water from a drainage area of 4 square miles. Completed in 1915, the structure is over a century 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. The most recent inspection on record was 08/01/2017.
Search for dams near your address to see all dams in your area with hazard classifications and safety data.
Location
| State | Montana |
| County | Missoula |
| Nearest City | Missoula |
| River/Stream | Tr-lake Creek |
| Coordinates | 47.03974, -113.91598 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 30 ft |
| Dam Height | 30 ft |
| Dam Length | 440 ft |
| Year Completed | 1915 (111 years old) |
Storage & Hydraulics
| NID Storage | 621 acre-ft |
| Max Storage | 621 acre-ft |
| Normal Storage | 143 acre-ft |
| Surface Area | 38 acres |
| Drainage Area | 4 sq mi |
| Max Discharge | 95 cfs |
| Spillway Type | Uncontrolled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | City of Missoula |
| Owner Type | Local Government |
| Hazard Classification | Significant |
| Condition Assessment | Not assessed |
| Last Inspection | 08/01/2017 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | MT01465 |
| Federal ID | MT01465 |
| More Info | State Dam Safety Program |