Marina Lagoon Reservoir Report

Last Updated: December 5, 2025

Marina Lagoon, also known as Seal Slough, is a crucial water resource in San Mateo, California, managed by the local government.


°F

°F

mph

Wind

%

Humidity

Summary

Built in 1953, this earth dam serves the primary purpose of flood risk reduction, while also offering recreational opportunities in the area. With a height of 17 feet and a hydraulic height of 14 feet, Marina Lagoon has a storage capacity of 1600 acre-feet and covers a surface area of 200 acres. Despite being labeled as low hazard potential, the dam is regularly inspected and deemed to be in satisfactory condition.

Located on the Belmont Slough in the San Francisco Bay area, Marina Lagoon plays a significant role in managing water flow and protecting the surrounding communities from flooding. The dam is regulated by the Department of Water Resources and the Safety of Dams agency in California, ensuring that it meets all state permitting, inspection, and enforcement requirements. While no spillway type or width is specified, the dam's construction and design reflect its effective flood risk reduction capabilities, contributing to the overall safety and resilience of the region.

With Congresswoman Jackie Speier representing the area, Marina Lagoon stands as a testament to effective water resource management and climate resilience efforts in California. As a key infrastructure for flood risk reduction, this earth dam not only safeguards communities but also provides a space for recreational activities, highlighting the harmonious coexistence of human development and environmental conservation. The continuous monitoring and maintenance of Marina Lagoon demonstrate a commitment to ensuring its long-term functionality and safety for generations to come.

Year Completed

1953

Dam Length

350

Dam Height

17

River Or Stream

Belmount Slough

Primary Dam Type

Earth

Surface Area

200

Hydraulic Height

14

Drainage Area

8.5

Nid Storage

1600

Hazard Potential

Low

Nid Height

17
       
Seasonal Comparison

Weather Forecast

Dam Data Reference

Condition Assessment

Satisfactory
No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.

Hazard Potential Classification

High
Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.