Oneida Main
Oneida Main is a concrete dam located in Franklin County, Idaho, built in 1920. It carries a High hazard potential classification and has a fair condition assessment.
About Oneida Main
The primary purpose of Oneida Main is irrigation. The dam stores and diverts water for agricultural irrigation, supporting farming operations in the surrounding area. The dam is owned by Pacificorp (private). It impounds the Bear River near Preston.
The dam stands 114 feet tall and stretches 420 feet across, creates a reservoir covering 357 acres, has a maximum storage capacity of 19,000 acre-feet, and collects water from a drainage area of 4,456 square miles. Completed in 1920, the structure is over a century old.
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 06/29/2022.
At 114 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 Idaho 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 | Idaho |
| County | Franklin |
| Nearest City | Preston |
| River/Stream | Bear River |
| Coordinates | 42.27570, -111.74970 |
Physical Characteristics
| Dam Type | Concrete |
| NID Height | 114 ft |
| Dam Height | 114 ft |
| Dam Length | 420 ft |
| Year Completed | 1920 (106 years old) |
Storage & Hydraulics
| NID Storage | 19,000 acre-ft |
| Max Storage | 19,000 acre-ft |
| Normal Storage | 10,880 acre-ft |
| Surface Area | 357 acres |
| Drainage Area | 4,456 sq mi |
| Max Discharge | 74,270 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Irrigation |
| Owner | PacifiCorp |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Fair |
| Last Inspection | 06/29/2022 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | ID00068 |
| Federal ID | ID00068 |
| More Info | State Dam Safety Program |