Narragansett Bay is a the largest bay and estuary in New England, second only to the Chesapeake Bay in all of the northeast US. On the southern end, Narragansett Bay opens into Rhode Island Sound and the North Atlantic Ocean. It is bound by land on two sides and its opening is guarded by Aquidneck Island and Conanicut Island, making it a natural harbor and strategically valuable location.

Of the many freshwater rivers that feed the bay, the Blackstone River is the largest. A small part of Narragansett Bay, where the Taunton River enters it, is in the state of Massachusetts, but all the rest is in Rhode Island. 

Because Narragansett Bay and its inlets cover roughly 15% of the total area of Rhode Island, the bay represents the state's defining geographic characteristic. The three largest population centers--Providence, Warwick and Cranston--border the bay in the northwest and the fourth largest--Pawtucket--is named for the falls that separate the freshwater Blackstone River from the saltwater Seekonk River, northernmost arm of the Bay.