A bay is an inlet of the sea. An estuary is a partially enclosed body of water where fresh water and salt water meet. Some bays—like the Chesapeake—are estuaries.

The Chesapeake Bay is the largest of more than 100 estuaries in the United States.

Estuaries are among the most productive environments on earth, creating more organic matter each year than similarly-sized forests and agricultural areas. Estuaries also provide diverse habitats for wildlife and aquatic life, protect our communities against flooding, reduce pollution to waterways, and support local economies through commercial and recreational activities.

An estuary is a partially enclosed body of water where fresh water from streams and rivers mixes with salt water from the ocean. Some river mouths are estuaries. For example, the tidal portion of the Hudson River in New York is an estuary.