River, northeastern U.S. and southeastern Canada.
Rising in northwestern Maine, it flows northeast to the Canadian border, then southeast to form that international boundary; in Canada, it flows through New Brunswick into the Bay of Saint John . It is 418 mi (673 km) long. At Grand Falls, Nfd., the river drops 75 ft (23 m), and at its mouth are the "reversing falls" rapids, caused by the strong tides of the bay, which at high tide force the river to reverse its flow.