Seal Slough, also known as Marina Lagoon, is a narrow winding tidal channel through a

tidal marsh A tidal marsh (also known as a type of "tidal wetland") is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean.

in San Mateo and

Foster City, California Foster City is a master-planned city located in San Mateo County, California, United States. Foster City is sometimes considered to be part of Silicon Valley for its local industry and its proximity to Silicon Valley cities. There are many n ...

. This

slough Slough () is a town in Berkshire, England, in the Thames Valley, west of central London and north-east of Reading, at the intersection of the M4, M40 and M25 motorways. It is part of the historic county of Buckinghamshire. In 2021, the ...

has been the object of a

wetland A wetland is a distinct semi-aquatic ecosystem whose groundcovers are flooded or saturated in water, either permanently, for years or decades, or only seasonally. Flooding results in oxygen-poor ( anoxic) processes taking place, especially ...

restoration project in recent years to enhance

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

value.

Dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing d ...

has been carried out in Seal Slough since at least 1954. When the original

sewage treatment plant Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...

for the city of San Mateo was constructed in 1935, its discharge was directed to Seal Slough. The marshy area through which Seal Slough meanders is a productive

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

wetland whose dominant

flora Flora (: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. The corresponding term for animals is ''fauna'', and for f ...

cordgrass ''Spartina'' is a genus of plants in the grass family, frequently found in coastal salt marshes. Species in this genus are commonly known as cordgrass or cord-grass, and are native to the coasts of the Atlantic Ocean in western and southern Eu ...

. There are a number of significant

wildlife Wildlife refers to domestication, undomesticated animals and uncultivated plant species which can exist in their natural habitat, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introdu ...

features associated with Seal Slough, including use by the

endangered An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...

California clapper rail.T.E. Harvey, H.S. Shellhammer, C.M.Hogan, K.Wilson, G.W.Ball, V. Pfeifle et al., ''Section 7 endangered species biological assessment for the proposed East Third Avenue widening project, city of San Mateo,

San Mateo County San Mateo County ( ), officially the County of San Mateo, is a county (United States), county located in the U.S. state of California. As of the 2020 United States census, the population was 764,442. Redwood City, California, Redwood City is th ...

'', prepared by Earth Metrics Inc. for

Caltrans The California Department of Transportation (Caltrans) is an Executive (government), executive department of the U.S. state of California. The department is part of the Government of California#State agencies, cabinet-level California State Tran ...

and the city of San Mateo, California (1980) A tide gate near the mouth of Seal Slough regulates tidal influx from

San Francisco Bay San Francisco Bay (Chochenyo language, Chochenyo: 'ommu) is a large tidal estuary in the United States, U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the cities of San Francisco, California, San ...

to Marina Lagoon; this flushing action is important to prevent

population explosion Overpopulation or overabundance is a state in which the population of a species is larger than the carrying capacity of its environment. This may be caused by increased birth rates, lowered mortality rates, reduced predation or large scale migr ...

midge A midge is any small fly, including species in several family (biology), families of non-mosquito nematoceran Diptera. Midges are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid ...

s in the local area.

Course

According to the City of San Mateo, Seal Slough properly refers to just the outlet, where it experiences a tidal exchange with San Francisco Bay on the eastern

shore A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...

line of the city of San Mateo, approximately midway between Coyote Point and the San Mateo Bridge. The portion upstream from the mouth is known as Marina Lagoon, which is approximately wide over a serpentine course long, representing the area that was diked and dredged starting from 1952 to provide a flood control basin and recreational area. The upstream inlets to Marina Lagoon, east of Hillsdale Boulevard, are O'Neill Slough and Belmont Slough. Officially, the entire waterway is still Seal Slough, as an act of Congress would be required to rename it. The

mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

is characterized by a marshy area and an extent of

bay mud Bay mud consists of thick deposits of soft, unconsolidated silty clay, which is saturated with water; these soil layers are situated at the bottom of certain estuary, estuaries, which are normally in temperate regions that have experienced cyclic ...

extending approximately northward into San Francisco Bay. The mouth is crossed by the Seal Slough Bridge carrying East Third Avenue / J Hart Clinton Drive, completed in 1985, and a narrower, older bridge previously used by the road and now part of the

San Francisco Bay Trail The San Francisco Bay Trail is a bicycle and pedestrian trail that when finished will allow continuous travel around the shoreline of San Francisco Bay. As of 2020, of the trail have been completed. When finished, the trail will be over of pa ...

. Seal Slough is separated from Marina Lagoon by a small earthen dam, which has tidal gates at the south end, and gravity or pumped flow at the north end. Near the downstream / northern end of Marina Lagoon is situated the city of San Mateo

Wastewater Treatment Plant Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...

, Bayside School, and Bayside/Joinville Park on the western/southern bank; on the northern/eastern bank is the Mariner's Island residential development. In between, a small island near the dam, accessible by boat, is preserved as Lagoon Island Park. The course of the slough is highly tortuous as it winds in a generally south-southeast direction. The channelized Leslie and Borel Creeks drain into Marina Lagoon. Further upstream, single-family residential uses have encroached closely on its southern/western banks; in this middle reach it also passes close to and north of Parkside School and Parkside Aquatic Park, approximately opposite from the Fashion Island shopping area. Further to the east it passes beside Lakeshore School and Lakeshore Park before crossing under Hillsdale Boulevard and entering Foster City. In the uppermost reaches, south of Los Prados Park (in San Mateo) and Boothbay Park (in Foster City), O'Neill and Belmont Sloughs drain into Marina Lagoon; O'Neill is channeled under U.S. 101.

Ecology

Much of the information regarding Seal Slough was developed in a 1980 study, in which

and the city retained Earth Metrics to analyze impacts of a new

bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...

across Seal Slough at East Third Avenue. The most significant habitat area along Seal Slough is the tidal mouth, where there are three identified

plant community A plant community is a collection or Association (ecology), association of plant species within a designated geographical unit, which forms a relatively uniform patch, distinguishable from neighboring patches of different vegetation types. The comp ...

zones. The lowest zone is defined by the presence of

mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal ...

s and/or the dominant plant

, '' distichlis'' sp. The middle zone is characterized by the dominant plant pickleweed, ''

Salicornia ''Salicornia'' is a genus of succulent, halophytic (salt tolerant) flowering plants in the family Amaranthaceae that grow in salt marshes, on beaches, and among mangroves. ''Salicornia'' species are native to North America, Europe, central Asia, ...

'' sp., and the upper zone, which is the most disturbed, is characterized by salt grass, ''Distichlis spicata'', and by peripheral

halophyte A halophyte is a salt-tolerant plant that grows in soil or waters of high salinity, coming into contact with saline water through its roots or by salt spray, such as in saline semi-deserts, mangrove swamps, marshes and sloughs, and seashores. ...

s (salt tolerant plants). The pickleweed community thrives primarily on the north banks of Seal Slough. Cordgrass and pickleweed habitats are among the most productive types in the state of California, in each case producing over five tons of organic material per acre per annum. Further these plants supply the adjacent mudflats with

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

that is the basis of

estuarine An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

food chain A food chain is a linear network of links in a food web, often starting with an autotroph (such as grass or algae), also called a producer, and typically ending at an apex predator (such as grizzly bears or killer whales), detritivore (such as ...

s. Cordgrass is also used for food and cover for a multiplicity of

waterfowl Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which i ...

, including the endangered California clapper rail, which species occurs in Seal Slough. Other avafauna found in this robust wetland include killdeer,

mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa. It has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Arge ...

s and the

snowy egret The snowy egret (''Egretta thula'') is a small white heron. The genus name comes from Provençal French for the little egret, , which is a diminutive of , 'heron'. The species name ''thula'' is the Araucano term for the black-necked swan, a ...

. The Seal Slough mudflats also provide a feeding area at high tides for a variety of

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

es including topsmelt,

anchovy An anchovy is a small, common forage fish of the Family (biology), family Engraulidae. Most species are found in marine waters, but several will enter brackish water, and some in South America are restricted to fresh water. More than 140 speci ...

bat ray The bat ray (''Myliobatis californica'') is an eagle rayGill, T.N. (1865). "Note on the family of myliobatoids, and on a new species of ''Aetobatis''". ''Ann. Lyc. Nat. Hist. N. Y.'' 8, 135–138."Myliobatis californica". Integrated Taxonomic Info ...

leopard shark The leopard shark (''Triakis semifasciata'') is a species of houndshark, in the family (biology), family Houndshark, Triakidae. It is found along the Pacific coast of North America, from the U.S. state of Oregon to Mazatlán in Mexico. Typically ...

spiny dogfish The spiny dogfish (''Squalus acanthias''), spurdog, mud shark, or piked dogfish is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several ...

striped bass The striped bass (''Morone saxatilis''), also called the Atlantic striped bass, striper, linesider, rock, or rockfish, is an anadromous perciform fish of the family Moronidae found primarily along the Atlantic coast of North America. It has ...

and longjaw mudsucker. Colonies of Australian tubeworms ('' ficopomatus enigmaticus'') were discovered on the support columns for SR 92 when the water level was lowered for maintenance. The worms were introduced inadvertently in the 1920s from ship bilge water.

References

External links

City of San Mateo: Description of Marina Lagoon and Seal Slough
* {{San Francisco Bay watershed Bodies of water of San Mateo County, California San Francisco Bay

Course

Ecology

See also

References

External links