Estuary

Regions of interaction between rivers and nearshore ocean waters, where tidal action and river flow create a mixing of fresh water and saltwater. These areas may include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife.


Source: Corrosion-Doctors.org

Wikipedia:  https://en.wikipedia.org/wiki/Estuary