Brackish water is water that is slightly to moderately saline. The salinity of brackish water varies from 0.5 to 16.
Brackish water is therefore oligohaline to mesohaline water.
Brackish water may be the result of the encounter of fresh and salt water, as in the estuary of a river, the melting of pack ice or even the dissolution of sedimentary rocks that have a high salt content.
Brackish water may also be the result of human activities, such as road gritting.
Brackish water can appear in an estuary, as in the La Gironde estuary. © Flikr, marycesyl, Creative Commons