Cape Breton Island is divided into four counties: Inverness, Victoria, Cape Breton, and Richmond and is joined to the mainland by the Canso Causeway, completed in 1955. This allows direct road and rail traffic to and from the island, enabling marine traffic to pass through the Canso Canal at the eastern end of the causeway.
Cape Breton's landscape is dominated by the Bras d'Or Lake system which the island wraps around, Boularderie Island, the Strait of Canso, and the Cape Breton Highlands, which are considered a continuation of the Appalachian chain.
Principal freshwater features are Lake Ainslie, the Margaree River system, and the Mira River. Innumerable smaller rivers and streams drain into the Bras d'Or Lake estuary and onto the Gulf of St. Lawrence and Atlantic coasts.