San Mateo County exists on the San Francisco Peninsula and is essentially divided by the Santa Cruz Mountain range with the San Francisco Bay to the east and the Pacific Ocean to the west. Historically, the bay side has provided forgiving climate, flat topography, and connectivity with San Francisco and Santa Clara Valley. Conversely, the coast side presented relatively harsher climates and mountainous terrain. Today there is an obvious difference in the amount of urban development between the San Mateo coast and bay sides. The bay side has experienced high amounts of urban development which required flood control modifications within nearby watersheds. Streams that once naturally flooded and meandered around hillsides before reaching the San Francisco Bay were hardscaped and straigtened into channels. However, the coast side of San Mateo County is mostly comprised of open space and agriculture land with sparsely distributed towns. The majority of watersheds on the coast side have little to no flood control modifications; however, water diversions, lack of riparian zone management, and water quality issues present challenges for these precious resources. 


Watershed Navigator

What watershed do you live in? Use our watershed navigator to learn more about your local watersheds. The watershed navigator is an interactive map which allows the user to learn more about a specific watersheds by clicking within the watershed boundary. For more information on bay side watersheds within San Mateo County including watershed maps, locations, and historical information, visit the interactive Guide to San Francisco Bay Area Creeks produced by the Oakland Museum.



Major Watersheds


Gazos Creek Watershed

Pescadero Marsh Gazos Creek is considered a priority watershed for steelhead and coho salmon recovery. Major tributaries include Old Womans Creek and Middle Fork Gazos Creek. Click here for more information.


Pilarcitos Creek Watershed

Pescadero Marsh Major tributaries include Arroyo Leon and Mills Creek. The San Francisco Public Utilities Commission manages the Pilarcitos Reservoir in the upper watershed. Click here for more information.


Pescadero Creek Watershed

Pescadero MarshThe Pescadero Creek Watershed is the largest watershed within San Mateo County. It consists of two major subwatersheds, Pescadero Creek and Butano Creek. The watershed also contains an impressive marsh inhabited by several native and protected species such as Steelhead, California red-legged frog, and San Francisco garter snake. The word Pescadero is of the Portugese language and translates to "fishing village". Click here for more information.

Colma Creek Watershed

Colma CreekThe headwaters of Colma Creek are on San Bruno Mountain. The lower reaches of Colma Creek are managed by the San Mateo County Flood Control District Click here for more information.


San Francisquito Creek Watershed

Pescadero Marsh Major tributaries include Los Trancos Creek, Corte Madera Creek, and Bear Gulch Creek. Los Trancos and San Francisquito form the boundary between San Mateo and Santa Clara counties Click here for more information.


San Gregorio Watershed

Pescadero Marsh

Major tributaries include El Corte de Madera Creek, Alpine Creek, and La Honda Creek. A small lagoon forms at the mouth of San Gregorio Creek during the dry season Click here for more information.


San Mateo Watershed

Pescadero MarshThe San Mateo Creek Watershed includes three reservoirs: San Andreas Lake, and Upper and Lower Crystal Springs Reservoirs, managed by the San Francisco Public Utilities Commission Click here for more information.


Belmont Creek Watershed

Pescadero Marsh Belmont Creek watershed originates east of the Pulgas Ridge in the hills above Hallmark Drive and is approximately 1,952 acres (3.1 sq mi) Click here for more information.


Atherton Creek Watershed

Pescadero MarshAtherton creek flows in its historical position from its headwaters just west of Interstate 280 to Alameda de las Pulgas. Further downstream, the creek is highly modified and flows through a concrete channel to El Camino Real and then a combination of concrete channel and culvert to San Francisco Bay. There are several small tributary creeks that drain into Atherton Creek above Alameda de las Pulgas, but further downstream the drainage network is comprised of underground culverts or storm drains. Click here for more information.