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Bull trout occur in the Mackenzie River Valley south of Great Bear Lake, and possibly also in some rivers north of this area. The species requires cold, clean water and populations can be resident or migratory. The latter can follow fluvial, adfluvial or anadromous life histories. Differences in habitat use by these populations and in the seasonal requirements of eggs, fry, juveniles, and adults are summarized. Spawning occurs in shallow, fast-flowing tributary streams with stable channels and gravel to boulder substrates, often in areas fed by groundwater that maintains suitable incubation and rearing conditions through the winter. To support the assessment, avoidance and mitigation of environmental impacts in the Mackenzie Valley, the potential impacts of development activities and climate change on survival of the species are reviewed. The species’ narrow habitat requirements for spawning and rearing make populations vulnerable to extirpation by habitat fragmentation and disruption. As slow-maturing but voracious predators, bull trout are also vulnerable to overharvesting and other stressors that target the older segment of the population. They do not compete well with other trout species at temperatures above 12 C, and are vulnerable to the introduction of other trout species.