Marina Lagoon

Our Aquatic Gem

San Mateo’s best-known secret is its tranquil, inviting Marina Lagoon (Lagoon). Enjoyed by our residents, watercraft users, beach enthusiasts, and families of bird species from pelicans to sandpipers, our Lagoon is an amenity for all.  

History – A Tidal Slough

A remnant of a tidal slough that was diked and dredged, our Lagoon now helps to protect our city from flooding, while offering a recreation area, wildlife, and ecological resource. Our staff manage the Lagoon optimize these benefits for all citizens. 

Marina Lagoon - Parkside Brochure Cover
Quick Facts
Inlet: O’Neill Slough
Outlet: Seal Slough
Distance: 4.5 miles
Width: 300’-400’
Depth: Average 3 feet
Watershed: 10.3 mi2
Flow: North, controlled

Water Flow & Levels

The Lagoon’s primary water source is tidal flow from San Francisco Bay through O’Neill Slough during high tides. Bay water is augmented by perennial low volume freshwater inflow from Laurel Creek, Borel Creek, and other lesser drainages within a 10.3 square mile watershed. During the wet season, stormwater runoff can comprise a larger proportion of inflow over the short-term, depending upon the size of the storm event. 

Find out more about water levels here.

  1. Water Quality
  2. Dredging
  3. Permits
  4. Vegetation
  5. Funding

Water Quality in the Marina Lagoon

Water quality is an important factor contributing to life on the Lagoon. The Lagoon receives stormwater runoff from a majority of the City, and pollutants are carried through streets and storm drains directly to it. These pollutants include pesticides applied to residential and commercial landscapes, oil and grease from cars, litter, legacy pollutants such as mercury, and bacteria from animals, sanitary sewer overflows, and leaks.

We are subject to several regulatory requirements that direct us to perform certain activities and develop plans to limit and address these pollutants. 

It is important to maintain healthy conditions for people who use the Lagoon area for recreational purposes, and for wildlife and fauna who make it their home.  

San Mateo storm drains flow directly to the Lagoon without water treatment. We take every opportunity to remind our residents to report stormwater pollution.  

Help us spread the word about the importance of keeping our stormwater clean.

Recent Presentations

Neighborhood UpdateMarina Logoon Pathway

Residents living near our Lagoon received an update in the mail in September 2021. Did we miss you? Email us to be added to our mailing list: marinaLagoon@cityofsanmateo.org.