Narragansett Bay is a bay and estuary on the north side of Rhode Island Sound. Covering 147 mi2 (380 km2) -- 120.5 mi2 (312 km2) 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 it extend into Massachusetts. Of over thirty islands in the Bay, the three largest ones are Aquidneck Island, Conanicut Island, and Prudence Island. Bodies of water that are part of Narragansett Bay include the Sakonnet River; Mount Hope Bay; and the southern, tidal part of the Taunton River. The bay opens on Rhode Island Sound — Block Island lies less than 20 miles (32 km) southwest of its opening — and the Atlantic Ocean. Narragansett Bay can be seen in NOAA chart 13221