What is brackish water?

Brackish water is more saline than freshwater but less than that of seawater. It mainly occurs when sea and freshwater mixes. 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 hence leading to a volume change of brackish water.

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

Some of the 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 a wide range of organisms like brackish fish, algae, shrimp, oysters, marsh grass, etc.

However, some seas and lakes are themselves already brackish, e.g., the Caspian Sea. Its salinity is 1/3 of the salinity in normal seawater. 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 change 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 mainly 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 where use their teeth to scrap algae from rocks. 

Scats live in freshwater when young and move to brackish water upon maturity. They are about 38 cm long and 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 levels of salinity.

Some species survive in saline water and brackish water. 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 of these plants can thrive to a specific limit of salinity.

Camboma alias fanwort is an aquarium plant that is very beautiful and has 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 concentration.

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 the specific gravity of brackish water accurately.