The Great Bras d'Or is a major saltwater channel connecting the vast, inland Bras d'Or Lake system to the North Atlantic Ocean. This tidal strait, with a surface area of 109 square kilometers, is characterized by its brackish waters, which vary in salinity from near-fresh at river mouths to nearly oceanic in its deeper sections. The channel is a deep, navigable waterway, with a maximum depth of 287 meters in the adjacent St. Andrews Channel, though the entrance to the ocean across the Great Bras d'Or Channel has a least depth of about 8 meters. The restricted nature of the channels dampens the tidal range compared to the open ocean. The surrounding landscape features steep hills rising to the Cape Breton Highlands on the northwestern side and includes extensive drumlin fields along the shallower western shores. This unique marine environment supports a diverse fishery within a UNESCO Biosphere Reserve.