The Piscataqua River, in the northeastern United States
, is a 12-mile (19 km) long tidal estuary formed by the confluence of the Salmon Falls and Cocheco rivers. The drainage basin of the river is approximately 1,495 square miles (3,870 km2), encompassing the additional watersheds of the Great Works River and five rivers flowing into Great Bay: the Bellamy, Oyster, Lamprey, Squamscott, and Winnicut.
The river runs southeastward, determining part of the boundary between the states of New Hampshire and Maine, and empties into the Atlantic Ocean east of Portsmouth, New Hampshire. The last six miles before the sea form Portsmouth Harbor, one of the finest harbors in the northeastern United States, despite a tidal current rated as one of the fastest in North America