What is Brackish Water?

Posted on May 31, 2018

Grace Cove in Charleston Harbor Estuary

Brackish water is water that has a salinity that lies somewhere between fresh water and salt water. The definition of brackish from Merriam-Webster is "somewhat salty."

Water can become brackish from mixing with seawater. Bodies of water near natural salt deposits may also become brackish. A chemical spill can also result in brackish water.

What is the Salinity of Brackish Water

A precise scale has not been set to determine the amount of salt in brackish water. A graphic on Wikipedia shows brackish water at .5-30 ppt (parts per thousand) with fresh water at 0-.5 ppt and seawater at 30-50 ppt. NOAA also uses this breakdown to signify brackish water.

Where Can Brackish Water be Found?

The Baltic Sea, the Caspian Sea and Lake Charles all contain brackish water. Estuaries are a well-known source of brackish water. Estuaries are the mouth of a river where the tide of the ocean meets with rivers or streams flowing into it. The image above shows Grace Cove, which is part of the Charleston Harbor estuary in South Carolina. Estuaries have rich ecosystems and can be home to unique species of fish, plants and animals. They are often very susceptible to environmental changes.

NOAA notes that the salinity of estuarine water is variable depending on the estuary and other conditions. They say, "estuarine water varies from estuary to estuary, and can change from one day to the next depending on the tides, weather, or other factors."

Here is more about estuaries from the U.S. Environmental Protection Agency.



Wikipedia has a list of estuaries by U.S. state here. Wikipedia also has a list of brackish bodies of water.

Image: NOAA