What is Brackish Water

by Jay | Updated on July 24th, 2022

What is brackish water?

Brackish water is more saline than freshwater but less than that seawater. It mainly occurs when sea and freshwater mix. It contains about 0.5 to 30 grams of salt per liter. Brackish water has a large variance of salinity. Rains cause the boundaries of salt and freshwater to move, leading to a volume change of salty water.

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A common occurrence of salty water is in river estuaries where freshwater meets the sea and mixes. In addition, some well-known estuaries influence water levels and attract brackish water fish and vegetation surrounding the water bodies. 

brackish water

Some well-known estuaries are the Amazon River, Chesapeake Bay, Fleet Lagoon, Hampton Roads, Hudson River, Thames Estuary, and many more.

Many estuaries are shallow and are exposed to sunlight. That creates hospitable conditions in the estuaries to support organisms like salty fish, algae, shrimp, oysters, marsh grass, etc.

However, some seas and lakes are already salty, e.g., the Caspian Sea. Its salinity is 1/3 of the salinity in normal seawater. Yet, it is the world’s largest lake.

Many brackish water bodies are hostile to the survival of organisms. Species found in brackish water are adapted to saline water survival. Salty brackish water is very fertile. Fish in brackish water are fat and healthy. These organisms have mechanisms that help them adapt to changes in salt concentration.

Some freshwater fish, e.g., redfish and striped bass, can explore brackish waters comfortably. The arrowhead and fahaka putter fish are brackish water species. They can grow up to 43 cm long and feed on snails and mussels.  

Gobies are common in brackish water (about 10 cm long) and live in tropical and temperate climates. You mainly find them in shallow marshes, mangrove swamps, and lower rivers, using their teeth to scrape algae from rocks. 

Scats live in freshwater when young and move to brackish water upon maturity. They are about 38 cm long and have a life expectancy of up to 20 years in healthy brackish water. They live on algae and feces.

Gars, alias garpikes, are highly scaled and have elongated bodies. They are mainly found in freshwater but travel through brackish water as they adapt to different salinity levels.

Some species survive in saline water and brackish water. This is because they cannot cross to freshwater.

Archerfish live in brackish water, predating on insects. They shoot water spouts from 1-2 meters away to knock down their prey. They can take multiple shots 5 meters away and get their prey.

Freshwater plants do well in brackish water. Some are anacharis, Cabomba, hornwort, wisteria, anubias, cryptocoryne, and Vallisneria. However, salinity in brackish water differs; hence, each plant can thrive to a specific limit of salinity.

Camboma, alias fanwort, is a very beautiful aquarium plant with rapid growth qualities. They are found in freshwater and low-saline level brackish water.  

Some plants that tolerate high salinity levels are C. Ciliata species of cryptocoryne. The majority of aquarium plants cannot endure such levels of salinity. They are also found in brackish water with higher concentrations.

The brackish level of the water can be best described by the specific gravity of the water density to that of pure water. Use a refractometer or hydrometer to measure brackish water’s specific gravity accurately.


Self assessed Germaphobe, specializing in everything water, water filters, health and nutrition. Diagnosed with Type 2 Diabetes, I've acquired immense amount of knowledge when it comes to natural, biology, and everything about human anatomy.