Lake Mission Viejo
Lake Mission Viejo is an earth dam located in Orange County, California, built in 1976. It carries a High hazard potential classification and has a poor condition assessment.
About Lake Mission Viejo
The primary purpose of Lake Mission Viejo 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 Lake Mission Viejo Association, Inc. (private). It impounds the Oso Creek near Mission Viejo.
The dam stands 123 feet tall and stretches 1,750 feet across, creates a reservoir covering 150 acres, has a maximum storage capacity of 4,300 acre-feet, and collects water from a drainage area of 3 square miles. Completed in 1976, the structure is 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. 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 04/16/2025.
At 123 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 | Orange |
| Nearest City | Mission Viejo |
| River/Stream | Oso Creek |
| Coordinates | 33.62710, -117.64920 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 123 ft |
| Dam Height | 123 ft |
| Dam Length | 1,750 ft |
| Year Completed | 1976 (50 years old) |
Storage & Hydraulics
| NID Storage | 4,300 acre-ft |
| Max Storage | 4,300 acre-ft |
| Surface Area | 150 acres |
| Drainage Area | 3 sq mi |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Lake Mission Viejo Association, Inc. |
| Owner Type | Private |
| Hazard Classification | High |
| Condition Assessment | Poor |
| Last Inspection | 04/16/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA01122 |
| Federal ID | CA01122 |
| More Info | State Dam Safety Program |