The isthmus separates the waters of Chignecto Bay, a sub-basin of the Bay of Fundy, from those of Baie Verte, a sub-basin of the Northumberland Strait that is an arm of the Gulf of St. Lawrence. The isthmus stretches from its northerly point at an area in the Petitcodiac River valley near the city of Dieppe, New Brunswick to its southerly point at an area near the town of Amherst, Nova Scotia. At its narrowest point between Amherst and Tidnish, the isthmus measures 24 kilometres wide. Because of its strategic position, it has been important to competing forces through much of its history of occupation.