Lewiston Dam is an earth dam located in Trinity County, California, built in 1963. It carries a High hazard potential classification.
Dam profile
NID height · 91 ft91 ft tall and 745 ft long, taller than 98% of U.S. dams with a recorded height. Height is drawn to scale against a ten-story building, about 100 ft; the profile is a generic embankment section and the water level is illustrative.
About Lewiston Dam
The primary purpose of Lewiston 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 Bureau of Reclamation (federal). It impounds the Trinity River.
The dam stands 91 feet tall and stretches 745 feet across, creates a reservoir covering 750 acres, has a maximum storage capacity of 14,660 acre-feet, and collects water from a drainage area of 718 square miles. Completed in 1963, the structure is well into its service life at over 50 years 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. An emergency action plan is in place for this dam. The most recent inspection on record was 04/19/2023.
At 91 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 California 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 | California |
| County | Trinity |
| River/Stream | Trinity River |
| Coordinates | 40.72640, -122.79300 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 91 ft |
| Dam Height | 73 ft |
| Dam Length | 745 ft |
| Year Completed | 1963 (63 years old) |
Storage & Hydraulics
| NID Storage | 14,660 acre-ft |
| Max Storage | 14,660 acre-ft |
| Normal Storage | 14,660 acre-ft |
| Surface Area | 750 acres |
| Drainage Area | 718 sq mi |
| Max Discharge | 1,902 cfs |
| Spillway Type | Controlled |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Bureau of Reclamation |
| Owner Type | Federal |
| Hazard Classification | High |
| Condition Assessment | Not assessed |
| Last Inspection | 04/19/2023 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA10165 |
| Federal ID | CA10165 |
| More Info | State Dam Safety Program |