Brackish water area is an area of rivers, lakes, marshes, and coastal waters occupied by brackish water. The Chinese character "汽" means "brackish," and the term "brackish water" refers to a mixture of freshwater and seawater.

Generally, the estuary where a river empties fresh water into the sea is considered to be brackish water. A deep bay is similar to this, and the landward part of a tidal flat is also brackish water.