From Longman Dictionary of Contemporary Englishbrackishbrack‧ish /ˈbrækɪʃ/ adjective SGbrackish water is not pure because it is slightly salty
Examples from the Corpus
brackish• A layer of photosynthetic bacteria lives permanently on the boundary between brackish and highly saline water.• All these tropical areas have their own brackish flora and fauna, but few if any are known in the trade.• Although most of the levels are freshwater, some are brackish in their more southerly parts.• Fresh or brackish lakes and lagoons, usually reed-fringed, also marshes.• These fishes do best in brackish or salt water.• My brackish water tank is built into a wall.• They hunt for camel meat by putting land mines around the region's brackish waterholes.• Amazon and others World-wide examples of these brackish waters abound.Origin brackish (1500-1600) Dutch brac “salty” 