The St John River, one in an extensive network of rivers in New Brunswick, flows from north to south in the western part of the province. It forms part of the border with Maine, as does the Saint Croix River.
St John River results in the Reversing Falls, where the force of the incoming tide reverses a series of low waterfalls where the river meets the sea. The water rushes uphill in a tidal wall against the normal flow of the falls, defying gravity. This exceptional tidal activity in the Bay of Fundy helps keep its ports ice-free in the winter.