Saint John Harbour is a large natural harbour on the Atlantic coast of New Brunswick, Canada, and within the seaport city of Saint John, New Brunswick located at the mouth of the Saint John River. Opening into the Bay of Fundy, it serves as one of the most important deep-water ports on the Atlantic coast of North America. The harbour has long been central to the city’s economic and cultural identity, supporting shipbuilding, trade, fishing, and energy industries since the 18th century. It is also home to the Port of Saint John, one of Canada’s major seaports, handling a wide range of cargo and cruise ship traffic. The harbour’s unique geography, including the famous Reversing Falls where the river’s flow is affected by powerful Fundy tides, makes it a notable natural and tourist feature of the region.