Stanley A. Mahr Reservoir
Stanley A. Mahr Reservoir is an earth dam located in San Diego County, California, built in 1981. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Stanley A. Mahr Reservoir
The primary purpose of Stanley A. Mahr Reservoir 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 Vallecitos Water District (public utility). It impounds the Tr Encinitas Cr near La Costa Oaks South.
The dam stands 79 feet tall and stretches 950 feet across, creates a reservoir covering 8 acres, has a maximum storage capacity of 166 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1981, the structure is 45 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. 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 04/03/2025.
At 79 feet, this dam is taller than 97% 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 | San Diego |
| Nearest City | La Costa Oaks South |
| River/Stream | Tr Encinitas Cr |
| Coordinates | 33.09420, -117.22300 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 79 ft |
| Dam Height | 79 ft |
| Dam Length | 950 ft |
| Year Completed | 1981 (45 years old) |
Storage & Hydraulics
| NID Storage | 166 acre-ft |
| Max Storage | 166 acre-ft |
| Surface Area | 8 acres |
| Drainage Area | 0 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Vallecitos Water District |
| Owner Type | Public Utility |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 04/03/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA01280 |
| Federal ID | CA01280 |
| More Info | State Dam Safety Program |