St. Helena Ler
St. Helena Ler is an earth dam located in Napa County, California, built in 1878. It carries a High hazard potential classification and has a poor condition assessment.
About St. Helena Ler
The primary purpose of St. Helena Ler 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 City Of Saint Helena (local government). It impounds the Tr Napa River near St. Helena.
The dam stands 44 feet tall and stretches 856 feet across, creates a reservoir covering 12 acres, has a maximum storage capacity of 210 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1878, 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 poor, meaning the dam has recognized safety deficiencies that require remediation to address risks. An emergency action plan is in place for this dam. The most recent inspection on record was 06/11/2025.
At 44 feet, this dam is taller than 90% 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 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 | Napa |
| Nearest City | St. Helena |
| River/Stream | Tr Napa River |
| Coordinates | 38.50730, -122.49120 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 44 ft |
| Dam Height | 44 ft |
| Dam Length | 856 ft |
| Year Completed | 1878 (148 years old) |
Storage & Hydraulics
| NID Storage | 210 acre-ft |
| Max Storage | 210 acre-ft |
| Surface Area | 12 acres |
| Drainage Area | 0 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | City of Saint Helena |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Poor |
| Last Inspection | 06/11/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00148 |
| Federal ID | CA00148 |
| More Info | State Dam Safety Program |