Spencer Lake
Spencer Lake is an earth dam located in San Mateo County, California, built in 1876. It carries a High hazard potential classification and has a satisfactory condition assessment.
About Spencer Lake
The primary purpose of Spencer Lake is flood risk reduction. The dam is designed to control downstream flooding by temporarily storing excess water during storms and releasing it at a controlled rate. The dam is owned by Town Of Hillsborough (local government). It impounds the Tr S Francisco Bay near Hillsborough.
The dam stands 87 feet tall and stretches 400 feet across, creates a reservoir covering 4 acres, has a maximum storage capacity of 73 acre-feet, and collects water from a drainage area of 0 square miles. Completed in 1876, 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 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 11/05/2025.
At 87 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 Mateo |
| Nearest City | Hillsborough |
| River/Stream | Tr S Francisco Bay |
| Coordinates | 37.57050, -122.37900 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 87 ft |
| Dam Height | 87 ft |
| Dam Length | 400 ft |
| Year Completed | 1876 (150 years old) |
Storage & Hydraulics
| NID Storage | 73 acre-ft |
| Max Storage | 73 acre-ft |
| Surface Area | 4 acres |
| Drainage Area | 0 sq mi |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | Town of Hillsborough |
| Owner Type | Local Government |
| Hazard Classification | High |
| Condition Assessment | Satisfactory |
| Last Inspection | 11/05/2025 |
| Emergency Action Plan | Yes |
Identifiers
| NID ID | CA00673 |
| Federal ID | CA00673 |
| More Info | State Dam Safety Program |