Marina Lagoon
Marina Lagoon is an earth dam located in San Mateo County, California, built in 1953. It carries a Low hazard potential classification and has a satisfactory condition assessment.
About Marina Lagoon
The primary purpose of Marina Lagoon 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 City Of San Mateo (local government). It impounds the Belmount Slough.
The dam stands 17 feet tall and stretches 350 feet across, creates a reservoir covering 200 acres, has a maximum storage capacity of 1,600 acre-feet, and collects water from a drainage area of 8 square miles. Completed in 1953, the structure is well into its service life at over 50 years old.
This dam has a low hazard potential classification, meaning that failure would cause minimal damage, limited primarily to the dam owner's property, with no expected loss of life. Its condition is rated satisfactory, indicating no existing or potential dam safety deficiencies are recognized. The most recent inspection on record was 10/01/2025.
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Location
| State | California |
| County | San Mateo |
| River/Stream | Belmount Slough |
| Coordinates | 37.56930, -122.29130 |
Physical Characteristics
| Dam Type | Earth |
| NID Height | 17 ft |
| Dam Height | 17 ft |
| Dam Length | 350 ft |
| Year Completed | 1953 (73 years old) |
Storage & Hydraulics
| NID Storage | 1,600 acre-ft |
| Max Storage | 1,600 acre-ft |
| Surface Area | 200 acres |
| Drainage Area | 8 sq mi |
Ownership & Safety
| Purpose | Flood Risk Reduction |
| Owner | City of San Mateo |
| Owner Type | Local Government |
| Hazard Classification | Low |
| Condition Assessment | Satisfactory |
| Last Inspection | 10/01/2025 |
| Emergency Action Plan | No |
Identifiers
| NID ID | CA01429 |
| Federal ID | CA01429 |
| More Info | State Dam Safety Program |