The Piscataqua River ((/pɪˈskætəkwə/)) is a 12-mile-long (19 km) tidal river forming the boundary of the U.S. states of New Hampshire and Maine from its origin at the confluence of the Salmon Falls River and Cochecho River to the Atlantic Ocean. The drainage basin of the river is approximately 1,495 square miles (3,870 km), including the subwatersheds of the Great Works River and the five rivers flowing into Great Bay: the Bellamy, Oyster, Lamprey, Squamscott, and Winnicut.
The river runs southeastward, with New Hampshire to the south and west and Maine to the north and east, and empties into the Gulf of Maine east of Portsmouth, New Hampshire. The last 6 miles (10Â km) before the sea are known as Portsmouth Harbor and have a tidal current of around 4 knots (7.4Â km/h; 4.6Â mph). Beyond the tidal currents, the river has a flood current speed of 12 knots, making it the fastest river on the eastern seaboard of the United States and one of the fastest rivers in the country. The cities/towns of Portsmouth, New Castle, Newington, Kittery and Eliot have developed around the harbor.