Fundy, Bay of, an arm of the Atlantic Ocean between the Canadian provinces of New Brunswick and Nova Scotia, eastward from Maine. The bay has a length of about 175 miles (280 km), a maximum width of 65 miles (105 km), and depths up to 300 feet (90 m). Large extensions of the bay include Minas Channel, Minas Basin, and Chignecto and Passamaquoddy bays.

Tides in the Bay of Fundy are among the highest in the world—as much as 53 feet (16 m) in the Minas Basin. At St. John, New Brunswick, the incoming tide causes the Reversing Falls on the St. John River. St. John is the bay's main port. Fundy National Park lies on the New Brunswick coast at the entrance to Chignecto Bay. The first French settlement attempted in Canada was made on the shore of the bay by Samuel de Champlain and the Sieur de Monts in 1604–05.