Lake trout are the largest trout native to North America. The largest lake trout on record weighed 46.3 kg (102 lb), which was caught by the commercial fishery at Lake Athabasca, Saskatchewan in 1961. The angling record contains a specimen weighing 32.8 kg (72.25 lb), caught in Great Bear Lake, Northwest Territories, in 1995. In Nova Scotia, the average lake trout caught is usually less than 2.0 kg (4.4 lb). A lake trout weighing 8.6 kg (19 lb) and measuring 81.3 cm (32 inches) was caught in Sherbrooke Lake, Nova Scotia in 1992.
Typically, lake trout are long and slender, with a deeply forked caudal fin. This distinguishes them from other chars, such as speckled or brook trout.
The overall coloration is light spots on a dark background, that varies from light green to almost black. Lake trout do not have the red spots found on speckled trout. Orange or red-orange may be present on the pelvic, pectoral, and, especially, anal fins, but this feature is usually more apparent in northern populations. A narrow white border is present on the lower fins, but it is never as immaculate or as wide as on the fins of a speckled trout. Dark bands may be noticeable on the sides of spawning males, but are not present in every population. Even during the mating season, the sexes can rarely be distinguished on the basis of color. Young lake trout or par have seven to twelve vertical bars on their sides. These are called par marks. The number of par marks varies, and the spaces between them are usually equal to or slightly greater than the width of an individual bar.