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Water Quality Control
By design, Marina Lagoon is the recipient of urban runoff, which typically contains a broad range of pollutants that have potential to adversely affect its water quality. The City conducts a stormwater pollution prevention program to help control and prevent pollutant loading to the lagoon. The program identifies and mitigates potential and actual sources of pollutants in runoff through a comprehensive program of business inspections, municipal maintenance practices, construction site controls, illicit discharge elimination, and public education.  Learn more about the City’s water pollution prevention programs.

Water quality is also maintained by maximizing the lagoon tidal water exchange rate. By doing so, bay-like conditions are maintained as much as possible to prevent development of thermal gradients, stagnant conditions, and lengthy periods of low salinity, and aquatic insect infestations. Water exchange also helps mix, dilute, and move pollutants in urban runoff through the system. A steady current through the lagoon is encouraged by setting the pumping rate to match the inflow. Normal operation results in an average water exchange of about 6 days. On rare occasions this scheme is altered to reserve floodwater storage capacity by closing the inlet gates, but is returned to open position as soon as it is prudent, depending upon stormwater inflows and tidal conditions.

Water samples are sampled each week at Lakeshore and Parkside Aquatic Park Beaches for concentrations of indicator bacteria. If concentrations of indicator bacteria exceed State or County standards, the area is posted to warn users that they may become ill if they engage in water contact activities in the posted area. 

For more information about the Beach Monitoring Program, visit the County's website.

Residents can help by limiting the amounts of fertilizers used on lawns; these may run-off into the lagoon and promote algae and bacteria growth. Also pick up pet waste, don't feed wildlife such as Canadian Geese, and keep your sewer laterals maintained, as these can also be sources of nutrients into the lagoon that contribute to the water quality problem.  

San Mateo City Hall – 330 West 20th Avenue, San Mateo, CA 94403

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