Narragansett Bay is a bay and estuary on the north side of Rhode Island Sound covering 147 square miles, 120.5 square miles of which is in Rhode Island. The bay forms New England's largest estuary, which functions as an expansive natural harbor and includes a small archipelago. Small parts of the bay extend into Massachusetts. There are more than 30 islands in the bay; the three largest ones are Aquidneck Island, Conanicut Island, and Prudence Island.