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

tidal Tidal is the adjectival form of tide. Tidal may also refer to: * Tidal (album), ''Tidal'' (album), a 1996 album by Fiona Apple * Tidal (king), a king involved in the Battle of the Vale of Siddim * TidalCycles, a live coding environment for music * ...

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. Tidal marshes are commonly zoned into lower marshes ( ...

in San Mateo and

Foster City, California Foster City is a city located in San Mateo County, California. The 2020 census put the population at 33,805, an increase of more than 10% over the 2010 census figure of 30,567. Foster City is sometimes considered to be part of Silicon Valley ...

. This

slough Slough () is a town and unparished area in the unitary authority of the same name in Berkshire, England, bordering west London. It lies in the Thames Valley, west of central London and north-east of Reading, at the intersection of the M4 ...

has been the object of a

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

restoration Restoration is the act of restoring something to its original state and may refer to: * Conservation and restoration of cultural heritage ** Audio restoration ** Film restoration ** Image restoration ** Textile restoration * Restoration ecology ...

project in recent years to enhance

habitat In ecology, the term habitat summarises the array of resources, physical and 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 ...

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 da ...

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

sewage treatment plant Sewage treatment (or domestic wastewater treatment, municipal wastewater treatment) is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable for discharge to the surrounding envir ...

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 is all the plant life present in a particular region or time, generally the naturally occurring (indigenous) native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' gut flora'' or '' skin flora''. E ...

cordgrass ''Spartina'' is a taxon of plants in the grass family, frequently found in coastal salt marshes. Its species are commonly known as cordgrass or cord-grass, and are native to the coasts of the Atlantic Ocean in western and southern Europe, north ...

. There are a number of significant

wildlife Wildlife refers to domestication, undomesticated animal species (biology), species, but has come to include all organisms that grow or live wilderness, wild in an area without being species, introduced by humans. Wildlife was also synonymous ...

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 and inva ...

California clapper rail Ridgway's rail (''Rallus obsoletus'') is a near-threatened species of bird. It is found principally in California's San Francisco Bay to southern Baja California. A member of the rail family, Rallidae, it is a chicken-sized bird that rarely flie ...

.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 located in the U.S. state of California. As of the 2020 census, the population was 764,442. Redwood City is the county seat, and the third most populated city following Daly ...

'', 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 Floodgates, also called stop gates, are adjustable gates used to control water flow in flood barriers, reservoir, river, stream, or levee systems. They may be designed to set spillway crest heights in dams, to adjust flow rates in sluices and c ...

near the mouth of Seal Slough regulates tidal influx from

San Francisco Bay San Francisco Bay is a large tidal estuary in the U.S. state of California, and gives its name to the San Francisco Bay Area. It is dominated by the big cities of San Francisco, San Jose, and Oakland. San Francisco Bay drains water from a ...

to Marina Lagoon; this flushing action is important to prevent

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

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

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 shore or a shoreline is the fringe of land at the edge of a large body of water, such as an ocean, sea, or lake. In physical oceanography, a shore is the wider fringe that is geologically modified by the action of the body of water past a ...

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 In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

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 estuaries, which are normally in temperate regions that have experienced cyclical glacia ...

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 p ...

. 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 used to remove contaminants from wastewater and convert it into an effluent that can be returned to the water cycle. Once returned to the water cycle, the effluent creates an acceptable impact on the environmen ...

, 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. Parkside Aquatic Park, San Mateo - 51793371320

Parkside Aquatic Park, San Mateo - 51793371320

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 U.S. Route 101, or U.S. Highway 101 (US 101), is a north–south United States Numbered Highway that runs through the states of California, Oregon, and Washington, on the West Coast of the United States. It is also known as (The Royal Roa ...

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 a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually somethi ...

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 of plant species within a designated geographical unit, which forms a relatively uniform patch, distinguishable from neighboring patches of different vegetation types. The components of each plant co ...

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 fl ...

s and/or the dominant plant

, ''

distichlis ''Distichlis'' is a genus of American and Australian plants in the grass family.Bell, H. L. & J. T. Columbus. 2008. Proposal for an expanded ''Distichlis'' (Poaceae, Chloridoideae): Support from molecular, morphological, and anatomical charact ...

'' 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. T ...

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 () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...

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 environment ...

food chain A food chain is a linear network of links in a food web starting from producer organisms (such as grass or algae which produce their own food via photosynthesis) and ending at an apex predator species (like grizzly bears or killer whales), det ...

Parkside Aquatic Park, San Mateo - 51792750338

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 in ...

, including the endangered

, which species occurs in Seal Slough. Other

avafauna Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight s ...

found in this robust wetland include

killdeer The killdeer (''Charadrius vociferus'') is a large plover found in the Americas. It was described and given its current scientific name in 1758 by Carl Linnaeus in the 10th edition of his ''Systema Naturae''. Three subspecies are described. T ...

mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and 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, app ...

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

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

es including

topsmelt The topsmelt silverside (''Atherinops affinis''), also known as the topsmelt, is a species of Neotropical silverside native to the eastern Pacific Ocean. Description The topsmelt silverside is a small, slim fish with a dorsally flattened body w ...

anchovy An anchovy is a small, common forage fish of the 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 species are placed in 1 ...

bat ray The bat ray (''Myliobatis californica'')Gill, 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. is an eagle ray found in muddy or sandy sloughs, estuaries and ...

leopard shark The leopard shark (''Triakis semifasciata'') is a species of houndshark, in the family Triakidae. It is found along the Pacific coast of North America, from the U.S. state of Oregon to Mazatlán in Mexico. Typically measuring 1.2–1.5 m (3.9� ...

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 (biology), family of sharks, which is part of the Squaliformes order. While these common names ma ...

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 al ...

and

longjaw mudsucker The longjaw mudsucker ''Gillichthys mirabilis'' is a goby (Gobiidae) of the Pacific Ocean coast of California and Baja California, noted for its extremely large mouth and ability to survive out of water for short periods. As the common name sugg ...

. Colonies of Australian tubeworms ('' ficopomatus enigmaticus'') were discovered on the support columns for SR92 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