Thunder Lake is an earth dam located in Cass County, Minnesota, built in 1934. It carries a Low hazard potential classification.
Dam profile
NID height · 18 ft18 ft tall. 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 Thunder Lake
The primary purpose of Thunder Lake is recreation. The dam creates a reservoir used for recreational activities such as fishing, boating, and swimming. The dam is owned by Mndnr-fisheries (state). It impounds the Willow River-tr near Boy River.
The dam stands 18 feet tall, creates a reservoir covering 1,347 acres, has a maximum storage capacity of 8,640 acre-feet, and collects water from a drainage area of 16 square miles. Completed in 1934, the structure is well-established, with more than 75 years of service.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. The most recent inspection on record was 07/18/2024.
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Location
| State | Minnesota |
| County | Cass |
| Nearest City | Boy River |
| River/Stream | Willow River-tr |
| Coordinates | 46.96047, -93.95298 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 18 ft |
| Dam Height | 18 ft |
| Year Completed | 1934 (92 years old) |
Storage & Hydraulics
| NID Storage | 8,640 acre-ft |
| Max Storage | 8,640 acre-ft |
| Normal Storage | 7,750 acre-ft |
| Surface Area | 1,347 acres |
| Drainage Area | 16 sq mi |
Ownership & Safety
| Purpose | Recreation |
| Owner | Mndnr-fisheries |
| Owner Type | State |
| Hazard Classification | Low |
| Condition Assessment | Not assessed |
| Last Inspection | 07/18/2024 |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | MN01091 |
| Federal ID | MN01091 |
| More Info | State Dam Safety Program |