Tongue River Dam
Tongue River Dam is an earth dam located in Big Horn County, Montana, built in 1939. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Tongue River Dam
The primary purpose of Tongue River 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 Tongue River near Ashland.
The dam stands 93 feet tall and stretches 1,824 feet across, creates a reservoir covering 3,700 acres, has a maximum storage capacity of 127,655 acre-feet, and collects water from a drainage area of 1,760 square miles. Completed in 1939, 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 satisfactory, indicating no existing or potential dam safety deficiencies are recognized. An emergency action plan is in place for this dam. The most recent inspection on record was 12/03/2024.
At 93 feet, this dam is taller than 98% of all dams in the United States.
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 | Big Horn |
| Nearest City | Ashland |
| River/Stream | Tongue River |
| Coordinates | 45.13250, -106.76963 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 93 ft |
| Dam Height | 93 ft |
| Dam Length | 1,824 ft |
| Year Completed | 1939 (87 years old) |
Storage & Hydraulics
| NID Storage | 127,655 acre-ft |
| Max Storage | 127,655 acre-ft |
| Normal Storage | 79,071 acre-ft |
| Surface Area | 3,700 acres |
| Drainage Area | 1,760 sq mi |
| Max Discharge | 98,000 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Irrigation |
| Owner | STATE WATER PROJECTS |
| Owner Type | State |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 12/03/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | MT00002 |
| Federal ID | MT00002 |
| More Info | State Dam Safety Program |