Coastal estuary systems start as freshwater streams high above the salt. This downwards flow of freshwater flows into and mixes with saltwater at some point, creating a zone of intermediate salinity known as the brackish zone before being overwhelmed by salt. This water with its intermediate salinity is somewhere between freshwater and saltwater, and is called brackish water.
To be exact, salinity is the measure of dissolved salt in water. Saltwater has on average about 35 g of dissolved salt per one litre of water i.e 3.5% salt, whereas, freshwater is classified as having 0.05% salt or less, with the main salts being sodium (Na +) and chloride (Cl −) ions).
The advantage of fishing in brackish water is that you have an opportunity to catch a variety of saltwater and freshwater species in the same area.
Brackish fish species are those that have a higher tolerance for varying levels of water salinity. Some species migrate between salt and fresh according to differing parts of their life cycles (bass being a prime example), whilst others seem to prefer the brackish zone for much of their lives. Whatever the case, prime brackish water targets
