Northern Pacific Reservoir Dam
Northern Pacific Reservoir Dam is a gravity dam located in Jefferson County, Montana, built in 1935. It carries a High hazard potential classification.
About Northern Pacific Reservoir Dam
The primary purpose of Northern Pacific Reservoir Dam 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 Ash Grove Cement (private). It impounds the Mcclellan Creek near East Helena.
The dam stands 35 feet tall and stretches 107 feet across, creates a reservoir covering 18 acres, has a maximum storage capacity of 173 acre-feet, and collects water from a drainage area of 33 square miles. Completed in 1935, the structure is well-established, with more than 75 years of service.
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.
At 35 feet, this dam is taller than 82% of dams nationwide.
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 Montana 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 | Montana |
| County | Jefferson |
| Nearest City | East Helena |
| River/Stream | Mcclellan Creek |
| Coordinates | 46.55407, -111.90546 |
Physical Characteristics
| Dam Type | Gravity |
| NID Height | 35 ft |
| Dam Height | 35 ft |
| Dam Length | 107 ft |
| Year Completed | 1935 (91 years old) |
Storage & Hydraulics
| NID Storage | 173 acre-ft |
| Max Storage | 173 acre-ft |
| Normal Storage | 48 acre-ft |
| Surface Area | 18 acres |
| Drainage Area | 33 sq mi |
| Max Discharge | 800 cfs |
Ownership & Safety
| Purpose | Water Supply |
| Owner | ASH GROVE CEMENT |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Not Rated |
| Emergency Action Plan | Not Required |
Identifiers
| NID ID | MT00858 |
| Federal ID | MT00858 |
| More Info | State Dam Safety Program |