Decoto Reservoir
Decoto Reservoir is an earth dam located in Alameda County, California, built in 1966. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Decoto Reservoir
The primary purpose of Decoto 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 Alameda County Water District (local government). It impounds the Offstream near Union City.
The dam stands 33 feet tall and stretches 1,360 feet across, creates a reservoir covering 3 acres, and has a maximum storage capacity of 46 acre-feet. Completed in 1966, 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. 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 10/29/2024.
At 33 feet, this dam is taller than 78% 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 | Alameda |
| Nearest City | Union City |
| River/Stream | Offstream |
| Coordinates | 37.59160, -121.99710 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 33 ft |
| Dam Height | 33 ft |
| Dam Length | 1,360 ft |
| Year Completed | 1966 (60 years old) |
Storage & Hydraulics
| NID Storage | 46 acre-ft |
| Max Storage | 46 acre-ft |
| Surface Area | 3 acres |
Ownership & Safety
| Purpose | Water Supply |
| Owner | Alameda County Water District |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/29/2024 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00898 |
| Federal ID | CA00898 |
| More Info | State Dam Safety Program |