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Brackish water, also sometimes termed brack water, is water occurring in a natural environment having more
salinity Salinity () is the saltiness or amount of dissolved in a body of , called (see also ). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important ...

salinity
than
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in ...
, but not as much as
seawater Seawater, or salt water, is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of E ...

seawater
. It may result from mixing seawater (salt water) with fresh water together, as in
estuaries An estuary is a partially enclosed coastal body of brackish water Brackish water, also sometimes termed brack water, is water occurring in a natural environment having more salinity File:IAPSO Standard Seawater.jpg, upInternational Associatio ...

estuaries
, or it may occur in brackish fossil
aquifer An aquifer is an underground layer of -bearing , rock fractures or unconsolidated materials (, , or ). can be extracted using a water . The study of water flow in aquifers and the characterization of aquifers is called . Related terms include a ...

aquifer
s. The word comes from the Middle Dutch root "
brak
brak
". Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment (see article on shrimp farms). Technically, brackish water contains between 0.5 and 30 grams of
salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...

salt
per litre—more often expressed as 0.5 to 30
parts per thousand In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowledge in the form of Testability, testable explanations and predictio ...
(‰), which is a
specific gravity Relative density, or specific gravity, is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemon ...
of between 1.0004 and 1.0226. Thus, ''brackish'' covers a range of salinity regimes and is not considered a precisely defined condition. It is characteristic of many brackish surface waters that their salinity can vary considerably over space or time. Water with a salt concentration greater than 30‰ is considered saline.


Brackish water habitats


Estuaries

Brackish water condition commonly occurs when fresh water meets seawater. In fact, the most extensive brackish water habitats worldwide are
estuaries An estuary is a partially enclosed coastal body of brackish water Brackish water, also sometimes termed brack water, is water occurring in a natural environment having more salinity File:IAPSO Standard Seawater.jpg, upInternational Associatio ...

estuaries
, where a river meets the sea. The
River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, se ...
flowing through
London London is the capital Capital most commonly refers to: * Capital letter Letter case (or just case) is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowerc ...

London
is a classic river estuary. The town of
Teddington Teddington is a suburb in south-west London in the London Borough of Richmond upon Thames. In 2021, Teddington was named as the best place to live in London by ''The Sunday Times''. Historically in Middlesex, Teddington is situated on a long mean ...
a few miles west of London marks the boundary between the tidal and non-tidal parts of the Thames, although it is still considered a freshwater river about as far east as
Battersea Battersea is a district of South London, South West London, England, within the London Borough of Wandsworth. It is located on the south bank of the River Thames, southwest of Charing Cross. History Historically a part of Surrey, Battersea w ...

Battersea
insofar as the average salinity is very low and the fish fauna consists predominantly of freshwater species such as
roach
roach
,
dace A dace is a small fish that can be one of many different species. The unmodified name is usually a reference to the common dace (''Leuciscus leuciscus''). This, like most fishes called "daces", belongs to the family Cyprinidae, mostly in subfamil ...
,
carp Carp are various species of oily fish, oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in ...

carp
,
perch Perch is a common name for fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. They form a sister group to the tunicates, together forming the Chordate#Taxo ...

perch
, and pike. The
Thames Estuary The Thames Estuary is where the River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in Engl ...
becomes brackish between Battersea and
Gravesend Gravesend is a town in northwest Kent, England, situated 21 miles (35 km) east-southeast of Charing Cross (central London) on the Bank (geography), south bank of the River Thames and opposite Tilbury in Essex. Located in the diocese of Ro ...
, and the diversity of freshwater fish species present is smaller, primarily roach and dace;
euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct relat ...
marine species such as
flounder Flounders are a group of flatfish species. They are demersal fish, found at the bottom of oceans around the world; some species will also enter estuary, estuaries. Taxonomy The name "flounder" is used for several only distantly related specie ...
,
European seabass The European bass (''Dicentrarchus labrax'') is a primarily ocean-going fish native to the waters off Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention ...

European seabass
, mullet, and
smelt Smelt may refer to: * Smelting, chemical process *The common name of various fish ** Smelt (fish), a family of small fish, Osmeridae ** Australian smelt in the family Retropinnidae and species ''Retropinna semoni'' ** Big-scale sand smelt ''Atherin ...
become much more common. Further east, the salinity increases and the freshwater fish species are completely replaced by euryhaline marine ones, until the river reaches Gravesend, at which point conditions become fully marine and the fish fauna resembles that of the adjacent
North Sea The North Sea is a sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
and includes both euryhaline and
stenohaline 200px, Goldfish ('' Carassius auratus'') are an example of a well known freshwater stenohaline fish. Stenohaline describes an organism, usually fish, that cannot tolerate a wide fluctuation in the salinity of water. Stenohaline is derived from the ...
marine species. A similar pattern of replacement can be observed with the aquatic plants and invertebrates living in the river. This type of
ecological succession Ecological succession is the process of change in the species structure of an community (ecology), ecological community over time. The time scale can be decades (for example, after a wildfire) or more or less. The community begins with relativel ...
from a freshwater to marine
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

ecosystem
is typical of river estuaries. River estuaries form important staging points during the migration of anadromous and catadromous fish species, such as
salmon Salmon is the common name for several species of ray-finned fish Actinopterygii ( New Latin ('having rays') + Greek ( 'wing, fins')), members of which are known as ray-finned fishes, is a clade A clade (; from grc, , ''klados'', ...

salmon
,
shad The Alosinae, or the shads,Alosinae
and
eel Eels are ray-finned fish Actinopterygii ( New Latin ('having rays') + Greek ( 'wing, fins')), members of which are known as ray-finned fishes, is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic gro ...
s, giving them time to form social groups and to adjust to the changes in salinity. Salmon are anadromous, meaning they live in the sea but ascend rivers to spawn; eels are catadromous, living in rivers and streams, but returning to the sea to breed. Besides the species that migrate through estuaries, there are many other fish that use them as "nursery grounds" for spawning or as places young fish can feed and grow before moving elsewhere.
Herring Herring are forage fish Forage fish, also called prey fish or bait fish, are small pelagic fish which are preyed on by larger predators for food. Predators include other larger fish, seabirds and marine mammals. Typical ocean forage fish feed ...

Herring
and
plaice Plaice is a common name for a group of flatfish that comprises four species: the European plaice, European, American plaice, American, Alaska plaice, Alaskan and scale-eye plaice. Commercially, the most important plaice is the European plaice, E ...
are two commercially important species that use the Thames Estuary for this purpose. Estuaries are also commonly used as fishing grounds, and as places for fish farming or ranching. For example,
Atlantic salmon The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae Salmonidae is a Family (biology), family of ray-finned fish, the only living family currently placed in the Order (biology), order Salmoniformes ...

Atlantic salmon
farms are often located in estuaries, although this has caused controversy, because in doing so, fish farmers expose migrating wild fish to large numbers of external
parasites Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is adaptation (biology), adapted structurally to this w ...

parasites
such as sea lice that escape from the pens the farmed fish are kept in.


Mangroves

Another important brackish water habitat is the
mangrove swamp A mangrove swamp is a distinct saline woodland A woodland () is, in the broad sense, land covered with trees, or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest A forest is ...

mangrove swamp
or mangal. Many, though not all, mangrove swamps fringe estuaries and lagoons where the salinity changes with each tide. Among the most specialised residents of mangrove forests are
mudskippers Mudskippers are amphibious fish 300px, Mudskippers (''Periophthalmus gracilis'' shown) are among the most land adapted of fish (excepting, from a cladistic perspective, tetrapods), and are able to spend days moving about out of water. Amphibiou ...

mudskippers
, fish that forage for food on land, and
archer fish The archerfish (spinner fish or archer fish) form a monotypic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular b ...
, perch-like fish that "spit" at insects and other small animals living in the trees, knocking them into the water where they can be eaten. Like estuaries, mangrove swamps are extremely important breeding grounds for many fish, with species such as snappers,
halfbeak Hemiramphidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the ...

halfbeak
s, and
tarpon Tarpons are fish of the genus ''Megalops''. They are the only members of the family Megalopidae. Of the two species, one (''M. atlanticus'') is native to the , and the other (''M. cyprinoides'') to the Oceans. Species and habitats The two s ...

tarpon
spawning or maturing among them. Besides fish, numerous other animals use mangroves, including such species as the
saltwater crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They f ...

saltwater crocodile
,
American crocodile The American crocodile (''Crocodylus acutus'') is a species of crocodilian Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanli ...

American crocodile
,
proboscis monkey The proboscis monkey (''Nasalis larvatus'') or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color and a long tail. It is Endemism, endemic to the southeast Asian island of Borneo and is foun ...

proboscis monkey
,
diamondback terrapin The diamondback terrapin or simply terrapin (''Malaclemys terrapin'') is a species of turtle native to the Brackish water, brackish coastal tidal marshes of the eastern and southern United States, and in Bermuda. It belongs to the monotypic genus ...
, and the crab-eating frog, ''Fejervarya cancrivora'' (formerly ''Rana cancrivora''). Mangroves represent important nesting site for numerous birds groups such as herons, storks, spoonbills, ibises, kingfishers, shorebirds and seabirds. Although often plagued with
mosquito Mosquitoes are members of a group of almost 3,600 species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defin ...

mosquito
es and other insects that make them unpleasant for humans, mangrove swamps are very important buffer zones between land and sea, and are a natural defense against hurricane and tsunami damage in particular. The
Sundarbans The Sundarbans is a mangrove A mangrove is a shrub or small tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves occur worldwide in the tropics ...

Sundarbans
and
Bhitarkanika Mangroves Bhitarkanika Mangroves is a mangrove A mangrove is a shrub or small tree that grows in coastal saline or brackish water. The term is also used for tropical coastal vegetation consisting of such species. Mangroves occur worldwide in the trop ...
are two of the large mangrove forests in the world, both on the coast of the
Bay of Bengal The Bay of Bengal is the northeastern part of the Indian Ocean The Indian Ocean is the third-largest of the world's five ocean The ocean (also the or the world ocean) is the body of that covers approximately 70.8% of the surface ...

Bay of Bengal
.


Brackish seas and lakes

Some seas and lakes are brackish. The
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean, enclosed by Denmark Denmark ( da, Danmark, ) is a Nordic country The Nordic countries, or the Nordics, are a geographical and cultural region In geography, regions are areas that a ...

Baltic Sea
is a brackish sea adjoining the
North Sea The North Sea is a sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
. Originally the
confluence In geography Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is ...

confluence
of two major river systems prior to the
Pleistocene The Pleistocene ( , often referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations. Before a change finally ...
, since then it has been flooded by the North Sea but still receives so much freshwater from the adjacent lands that the water is brackish. Because the salt water coming in from the sea is denser than freshwater, the water in the Baltic is stratified, with salt water at the bottom and freshwater at the top. Limited mixing occurs because of the lack of tides and storms, with the result that the fish fauna at the surface is freshwater in composition while that lower down is more marine.
Cod Cod is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is sometim ...

Cod
are an example of a species only found in deep water in the Baltic, while are confined to the less saline surface waters. The
Caspian Sea The Caspian Sea (also known as Mazandaran Sea, Hyrcanian Ocean, or Khazar Sea), tk, Hazar deňzi, az, Xəzər Dənizi, russian: Каспийское море, script=Latn, fa, دریای مازندران، دریای خزر, script=Latn, tly, ...

Caspian Sea
is the world's largest lake and contains brackish water with a salinity about one-third that of normal
seawater Seawater, or salt water, is water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of E ...

seawater
. The Caspian is famous for its peculiar animal fauna, including one of the few non-marine seals (the
Caspian seal The Caspian seal (''Pusa caspica'') is one of the smallest members of the earless seal family and unique in that it is found exclusively in the brackish Caspian Sea. They are found not only along the shorelines, but also on the many rocky islands ...
) and the great
sturgeon Sturgeon is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is s ...

sturgeon
s, a major source of
caviar Caviar (also known as caviare; from fa, خاویار, khâvyâr, egg-bearing) is a food consisting of salt-cured roe of the family Acipenseridae. Caviar is considered a delicacy and is eaten as a garnish or a spread. Traditionally, the term ...

caviar
.
Hudson Bay Hudson Bay ( iu, text=ᑲᖏᖅᓱᐊᓗᒃ ᐃᓗᐊ, translit=Kangiqsualuk ilua or iu, text=ᑕᓯᐅᔭᕐᔪᐊᖅ, translit=Tasiujarjuaq; french: baie d'Hudson), sometimes called Hudson's Bay (usually historically), is a large body of sal ...
is a brackish
marginal sea This is a list of seas of the World Ocean The ocean (also the sea or the world ocean) is the body of Saline water, salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Water distribution on Earth, Earth's w ...
of the
Arctic ocean The Arctic Ocean is the smallest and shallowest of the world's five major s. It spans an area of approximately and is also known as the coldest of all the oceans. The (IHO) recognizes it as an ocean, although some call it the Arctic Medit ...

Arctic ocean
, it remains brackish due its limited connections to the open ocean, very high levels freshwater
surface runoff Surface runoff (also known as overland flow) is the flow of water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it ac ...
input from the large
Hudson Bay drainage basin The Hudson Bay drainage basin is the drainage basin in northern North America where surface water empties into Hudson Bay and adjoining waters. Spanning an area of about , the basin is almost totally in Canada (spanning parts of the Canadian Prair ...
, and low rate of evaporation due to being completely covered in ice for over half the year. In the
Black Sea , with the skyline of Batumi Batumi (; ka, ბათუმი ) is the second largest city of Georgia Georgia usually refers to: * Georgia (country) Georgia ( ka, საქართველო; ''Sakartvelo''; ) is a country locat ...

Black Sea
the surface water is brackish with an average salinity of about 17-18 parts per thousand compared to 30 to 40 for the oceans. The deep,
anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of disso ...
water of the Black Sea originates from warm, salty water of the
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western Europe, Western and Southern Europe and Anatolia, on the south by North Africa ...

Mediterranean
.
Lake Texoma Lake Texoma is one of the largest reservoir A reservoir (; from French French (french: français(e), link=no) may refer to: * Something of, from, or related to France France (), officially the French Republic (french: link=no, Répub ...
, a reservoir on the border between the U.S. states of
Texas Texas (, ; Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambigu ...

Texas
and
Oklahoma Oklahoma () is a U.S. state, state in the South Central United States, South Central region of the United States, bordered by the state of Texas on the south and west, Kansas on the north, Missouri on the northeast, Arkansas on the east, New ...
, is a rare example of a brackish lake that is neither part of an
endorheic basin An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin A drainage basin is any area of land where precipitation In meteorology Meteorology is a branch of the atmospheric sciences Atmospheri ...
nor a direct arm of the ocean, though its salinity is considerably lower than that of the other bodies of water mentioned here. The reservoir was created by the damming of the
Red River of the South The Red River, or sometimes the Red River of the South, is a major river in the Southern United States The Southern United States, also referred to as the Southern States, the American South, Dixie, the Southland, or simply the South, is a ...
, which (along with several of its tributaries) receives large amounts of salt from natural seepage from buried deposits in the upstream region. The salinity is high enough that
striped bass The striped bass (''Morone saxatilis''), also called the Atlantic striped bass, striper, linesider, rock, or rockfish, is an anadromous Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, an ...

striped bass
, a fish normally found only in salt water, has self-sustaining populations in the lake.


Brackish marsh


Other brackish bodies of water

*


Terminology

Brackish water is referred to as brack water in some sources and places.


See also

*
List of brackish bodies of water Bodies of water of brackish water, brackish nature are found around the world in a wide variety of settings, shapes and sizes. The following is a list of notable bodies of brackish water. Brackish seas * Baltic Sea (the world’s largest inland br ...
* * * *


References


Further reading


Moustakas, A. & I. Karakassis. How diverse is aquatic biodiversity research?, Aquatic Ecology, 39, 367-375
{{Authority control Liquid water Aquatic ecology Coastal geography *