Final answer:
An estuary is divided into different zones based on the salinity of the water. The zone with the least saline water is called the freshwater zone.
Step-by-step explanation:
An estuary is a coastal area where freshwater from rivers and streams meets and mixes with saltwater from the ocean. It is divided into different zones based on the salinity of the water. The zone of an estuary that has the least saline water is called the freshwater zone or the riverine zone.
Learn more about Estuary zones