Yellow Water Main Dam
Yellow Water Main Dam is a rockfill dam located in Petroleum County, Montana, built in 1938. It carries a High hazard potential classification and has a fair condition assessment.
About Yellow Water Main Dam
The primary purpose of Yellow Water Main Dam is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by State Water Projects (state). It impounds the Yellow Water Creek near Mosby.
The dam stands 37 feet tall and stretches 1,695 feet across, creates a reservoir covering 490 acres, has a maximum storage capacity of 6,695 acre-feet, and collects water from a drainage area of 55 square miles. Completed in 1938, 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. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 10/25/2023.
At 37 feet, this dam is taller than 84% 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 | Petroleum |
| Nearest City | Mosby |
| River/Stream | Yellow Water Creek |
| Coordinates | 46.90230, -108.47120 |
Physical Characteristics
| Dam Type | Rockfill |
| NID Height | 37 ft |
| Dam Height | 37 ft |
| Dam Length | 1,695 ft |
| Year Completed | 1938 (88 years old) |
Storage & Hydraulics
| NID Storage | 6,695 acre-ft |
| Max Storage | 6,695 acre-ft |
| Normal Storage | 3,835 acre-ft |
| Surface Area | 490 acres |
| Drainage Area | 55 sq mi |
| Max Discharge | 3,900 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Irrigation |
| Owner | STATE WATER PROJECTS |
| Owner Type | State |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 10/25/2023 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | MT00012 |
| Federal ID | MT00012 |
| More Info | State Dam Safety Program |