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.
Estuaries
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.
Mangroves
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.
Brackish seas
- Baltic Sea (the world’s largest pool of brackish water)
- Black Sea
- Caspian Sea (world’s largest lake)
Brackish water lakes
- Lake Charles in Lake Charles, Louisiana, USA
- Chilika Lake, Odisha, India
- Pangong Tso (Lake) in Ladakh, Jammu and Kashmir, India
- Lake Van, Turkey
Coastal lagoons, marshes, and deltas
- The Burgas Lakes near the Bulgarian Black Sea Coast
- Kaliveli Lake, near Pondichery, India
- Kerala Backwaters, Series of lagoons and lakes in Kerala
- Lagos Lagoon in Lagos, Nigeria
- Lake Pontchartrain, north of New Orleans, Louisiana, USA
- Pulicat Lake, north of Chennai, India
- The Rann of Kutch, on the border of India and Pakistan
- Parts of the Rhône Delta, France: An area known as the Camargue
Estuaries
- Amazon River, empties so much freshwater into the Atlantic Ocean that it reduces the salinity of the sea for hundreds of miles
- Chesapeake Bay, in Maryland, USA
- The Fleet lagoon, Dorset, England
- Hampton Roads, Virginia, USA
- Lower Hudson River, in New York and New Jersey, USA
- Lingding Yang, Guangdong, the People's Republic of China
- Port Royal Sound part of Beaufort County, South Carolina, USA Archived 2015-07-10 at the Wayback Machine
- Saint Lawrence and Saguenay Rivers, the part downstream from Québec and Saguenay respectively
- The Thames Estuary in South East England
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