Barkley Sound consists of three main channels, seaward extensions of a group of narrow fjord inlets at the northeast end of the sound. The largest of these, Alberni Inlet, continues seaward as Trevor Channel, with a sill extending across the mouth of Barkley Sound. The three prominent shallow banks near Barkley Sound, Amphitrite, La Perouse and Swiftsure, as well as the adjacent deep basins, are a result of the strong glacial influence on this area. The regional climate, characterized by mild temperatures and heavy winter rains, promotes a luxurious temperate rain forest with dense undergrowth. The mean annual rainfall is 270 cm with the heaviest rains occurring from November to February.
Snowfalls are rare.
The driest months are July and August. Winter storms can be expected from late October to mid-March. Water clarity varies throughout the year with reduced visibility during the plankton blooms of the summer months. The lowest tides occur during the evenings in winter, and the mornings in summer. The maximum predicted amplitude is 3.9 meters.