Located on the Arctic Circle (66!|0'N), Great Bear Lake is the largest lake within the borders of Canada. With its almost equally large companion, Great Slave Lake, and their combined drainage, the Mackenzie River, this water system completely dominates the geography of the Mackenzie District of the Northwest Territories.

Great Bear Lake lies across the junction between two major physiographic regions: the Kazan portion of the Canadian Shield and the Interior Plains (1). Originally formed by the broadening and deepening of preglacial valleys by erosional effects of ice during the Pleistocene (2), the lake has subsequently been altered by changes in the land form resulting from rebound following melting of the ice.

Precambrian rocks of the Shield form the eastern margin of McTavish Arm (3). This region of the lake has magnificent scenery amongst the many islands and long fjord-like indentations of the coastline. The complex rocks of the Precambrian are made up of sedimentary and metamorphic deposits supplemented by igneous intrusions forming dykes and sills (4, 5, 6, 7). Between the Shield and the Interior Plains region which forms most of the western shoreline, there is a narrow band of Ordovician rocks composed of limestone and dolomite with sandstone and conglomerate inclusions (8). The Great Bear Plain (8, 9) is largely composed of glacial till underlain with Mesozoic strata of undivided limestone. The terrain in this region is gently rolling, generally below 300 m in elevation with occasional hills such as Grizzley Bear Mountain or the Scented Grass Hills reaching an elevation of 450 m.

At the height of the most recent glaciation the majority of the land to the east of the Mackenzie River was covered by the Laurentide ice-sheet, but an unglaciated region is known to have existed to the west of Great Bear Lake along the front dividing the Laurentide from the Cordilleran ice-sheets (10). About 10,000 years B. P. the ice-margin approximately coincided with the Shield boundary (11). The ice-sheet crossed the basic northward slope of the land blocking drainage thus giving rise to the very large proglacial lake, Glacial Lake McConnell, covering the area now occupied by both Great Bear and Great Slave Lakes and the land between them (12, 13). This immense lake drained to the south-east; its strand-lines, still visible 145 m above the present level of Great Bear Lake, attest to its original size. With the retreat of the ice the land rebounded unequally causing a noticeable tilt to the strand-lines and the formation of an outlet at the western end of what is now Smith Arm. As the land surface continued to change the outlet switched from this region to its present location at the western end of Keith Arm. Archaeological evidence suggests this outlet was established by about 4000 B. P., some 12 m above the present lake level. Further archaeological evidence indicates that the present lake level had been established by about 2600 years B. P. (14, 15).

At the present time Great Bear Lake occupies a position close to the northern limit of trees. To the south and west are forests, largely of black and white spruce interspersed with muskeg in the lower-lying poorly drained regions. To the north the forest declines giving way to tundra with trees in the more sheltered areas only.

In Pre-European times the area was occupied by various Indian tribes of the Athapascan language group: the Hares on the north-western shore, Slaveys and Mountain people in the vicinity of Bear River, Dogribs along the southern- eastern shores and Copper Indians in the east, together making up a group recognised as the Satudene (15, 16). The northern shores of the lake were occasionally visited by the Inuit on hunting forays from the Coronation Gulf region.

The first European penetration was the establishment of a fur-trading post by the Northwest Fur Company in 1799 (17, 18). Initial geological investigations in the region were carried out in 1898 by Dr. J. Mackintosh Bell and Charles Camsell (19). They noted the possibility of valuable metal ores on the eastern shores of McTavish Arm (19). In 1903 E. A. Preble entered the region via the Camsell River, a route pioneered by Charles Camsell a year or two earlier (20). Preble (21) collected birds and fishes along the south sides of MCTavish and Keith Arms, adding considerably to the natural history of the region. In 1930 Gilbert LaBine staked claims for silver and cobalt at Echo Bay. A mine was established but it was found that the associated pitchblende deposits had the relatively high radium content of 1 g/6.5 tons of ore (22). The uranium ore was discarded as of little commercial value. With the advance of physics the demand for radium declined, production became unprofitable and the mine was closed in 1940. However, the mine was re-opened in 1942 by Eldorado Mining and Refining Company to supply uranium for the Manhatten Project. Quantities of uranium were to be found in the tailings from the radium extraction process which, having previously been dumped in the lake, were recovered by dredging. This mine was closed in 1964 but certain workings were maintained for the extraction of silver by Echo Bay Mines Ltd.

The first biological survey of the lake, sponsored by the Fisheries Research Board of Canada, was carried out by Miller and Kennedy in 1945 (23, 24, 25). Thereafter, between 1963 and 1965 the Fisheries Research Board carried out a more detailed biological and limnological survey (26, 27, 28). This three- year programme utilized the former mine tugboat M. V. Radium Gilbert as the survey ship. The relatively large size of this vessel enabled a bathymetric survey to be made as well as detailed investigations of temperature structure in the deepest regions. Investigations that have had a bearing on the lake circulation and theoretical aspects of the temperature of maximum density of fresh water with increasing pressure (29, 30). Observations on fish, plankton and benthos distribution and density also were made.

The northerly latitude of Great Bear Lake, combined with its great volume and immense heat budget (40,600 cal cm-2)(26), ensure that it has many of the characteristics of a polar lake although in a northern continental setting. This appears to account for anomalies with respect to the fish species complement. Despite the general correlation between increasing lake size and increasing species richness (32) when the effect of latitude is removed, Great Bear Lake exhibits the opposite effect: fewer species in the lake than might be expected and fewer species in the lake than exist within the drainage basin as a whole. This is manifest in several ways: 1) all species except lake trout Salvelinus namaycush and deep-water sculpin Myoxocephalus quadricornis are confined to the warmer shallower more secluded bays, 2) certain species occurring both upstream and downstream of the lake do not occur in the lake itself (lake chub Couesius plumbeus and troutperch Percopsis omiscomaycus) and 3) other species occur in only very limited locations (walleye Stizostedion vitreum or at very small size (relative to neighbouring lakes) and at very few locations (burbot Lota lota). This is a very clear-cut case of environmental exclusion.