The majority of the lands comprising the isthmus have low elevation above sea level; a large portion comprises the Tantramar Marshes, as well as tidal rivers, mud flats, inland freshwater marshes, coastal saltwater marshes, and mixed forest. Several prominent ridges rise above the surrounding low land and marshes along the Bay of Fundy shore, namely the Fort Lawrence Ridge (in Nova Scotia), the Aulac Ridge, the Sackville Ridge, and the Memramcook Ridge (in New Brunswick).
In contrast to the Bay of Fundy shoreline in the west, the Northumberland Strait shoreline in the east is largely forested, with serpentine tidal estuaries such as the Tidnish River penetrating inland. The narrowest point on the Northumberland shoreline is opposite the Cumberland Basin at Baie Verte. If sea levels were to rise by 12 meters, the isthmus would be flooded, effectively making mainland Nova Scotia an island.