Killer whales are found in all three of Canada's oceans, as well as occasionally in Hudson Bay and the Gulf of St. Lawrence. It is not limited by such habitat considerations as depth, water temperature or salinity. They have been seen in water ranging from shallow (several metres deep) to open ocean depths. The offshore population is small and is poorly studied. Some individuals have been sighted as far south as central California and as far north as Alaska.

Resident killer whales live in separate northern and southern communities. The northern community lives off northern Vancouver Island and the mainland coast as far north as southeast Alaska. Southern residents are found off southern Vancouver Island.

The killer whale's size―seven to nine metres long and between four and five tonnes in weight―and distinctive black and white pattern makes its unmistakable. The first sight of a killer whale is often the tall dorsal fin, which may reach up to 1.8 metres in height in mature males. In females and young whales, the fin is smaller and crescent-shaped. Behind the dorsal fin is a grey area called a saddle patch. The shape of the dorsal fin and saddle patch, as well as natural nicks and scars on them, are unique to each killer whale. Calves are born measuring 2.5 metres but grow to reach lengths of up to 7.7 metres (females) to 9 metres (males). With no natural predators, killer whales can live to between 50 and 80 years of age. However, mortality between the ages of birth to six months can be as high as 50 per cent. High levels of mortality among newborn whales leads to average life spans of only 17 years for males and 29 years for females. Sexual maturity of killer whales is reached by approximately 15 years of age.