Brackish water

water with salinity between freshwater and sea
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Brackish water (less commonly brack water) is salt water and fresh water mixed together. It is saltier than fresh water, but not as salty as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers.

Some human activities can produce brackish water, mostly certain civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish pools for freshwater prawns.

Technically, brackish water contains between 0.5 and 30 grams of salt per litre—more often expressed as 0.5 to 30 parts per thousand (ppt or ‰). 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 and/or time.

Water salinity based on dissolved salts in parts per thousand (ppt)
Fresh water Brackish water Saline water Brine
< 0.5 0.5—35 35—50 > 50



The term brackish water comes from the Low German word Brack, which is a small lake made when a storm tide breaks a dike and floods land behind the dike.

Brackish water habitats



A brackish water fish: Monodactylus argenteus

The most important brackish water habitats are estuaries, where a river meets the sea, mixing salt and fresh water. The River Thames flowing through London is one of the most familiar of river estuaries.



Another important brackish water habitat is the mangrove swamp or mangal.

Brackish seas and lakes


Some seas and lakes are brackish. The Baltic Sea is a brackish sea adjoining the North Sea.

The Caspian Sea is the world's largest lake and contains brackish water with a salinity about one-third that of normal seawater. The Caspian is famous for its peculiar animal fauna, including one of the few non-marine seals (the Caspian seal) and the great sturgeons, the source of caviar.

Important brackish bodies of water


Brackish seas

Brackish water lakes

Coastal lagoons, marshes, and deltas