Lake trout (Salvelinus namaycush) is a freshwater char living mainly in lakes in northern North America. Other names for it include mackinaw, lake char (or charr), touladi, togue, and grey trout. In Lake Superior, they can also be variously known as siscowet, paperbellies and leans. Lake trout are prized both as game fish and as food fish.
From a zoogeographical perspective, lake trout are quite rare. They are native only to the northern parts of North America, principally Canada. Approximately 25% of the world's lake trout lakes are found in the province of Ontario. Even at that, only 1% of Ontario's lakes contain lake trout.

Lake trout are the largest of the charrs, the record weighing almost 46.3 kg (102 lb). They were fished commercially in the Great Lakes until lampreys, overharvest and pollution severely reduced the stocks. The lake trout is a slowly growing fish. It is also very late to mature. Populations are extremely susceptible to overexploitation. Lake trout are dependent on cold, oxygen-rich waters. They are nearer the surface during the period of summer stratification often living at depths of 20-60 m (60-200 ft).

It is generally accepted that there are two basic types of lake trout populations. Some lakes do not have forage fish during the period of summer stratification. In these lakes, lake trout populations are highly abundant, grow very slowly and mature at relatively small size. In those lakes that do contain deep water forage, lake trout grow much more quickly, mature at a larger size and are less abundant.

Lake trout have been known, very rarely, to hybridise in nature with the brook trout, but such hybrids are almost invariably reproductively sterile. Hybrids, known as "splake" are also artificially propagated in hatcheries and then planted into lakes in an effort to provide sport fishing opportunities.

The biological word: namaycush derives from an indigenous North American name for the species, most likely Ojibwe: namegos = "lake trout"; namegoshens = "rainbow trout".