The Foster City Lagoon as a drainage detention basin is designed to withstand successfully a storm of 100 year return frequency, or a storm of such severity that it is likely to occur only once each century.

The lagoon therefore provides maximum drainage security for Foster City citizens and businesses. Stormwater collected throughout the City flows to the Foster City Lagoon that serves as a drainage detention basin for the storm water runoff. The lagoon is designed and operated to store runoff from a 100-year storm event. All storm water enters the storm drain system through curb inlets and catch basins and drains into the lagoon from which it is pumped into the bay.

How well does the Foster City Lagoon system work as a drainage catch basin? During the El Nino rainstorms of 1997/98, which were very close to a 100-year frequency severity, the city of Foster City experienced no flooding while surrounding cities in San Mateo County experienced major drainage problems. Thanks to the effectiveness of its lagoon system, Foster City has never experienced major flooding.

It is unlawful to dispose of any substances that may contaminate the Lagoon and storm water system or cause blockages of the storm drainage system. In the event of flooding due to a blockage of the storm drain system, contact the Foster City Street Department.