Great Slave Lake

The Geographical Names Board of Canada records Great Slave Lake and Grand lac des Esclaves as the official English and French names for one lake polygon in the Northwest Territories. Its published coordinate is useful for small-scale mapping only: the database assigns it 1:5,000,000 relevance and warns that a polygon boundary may not align with a base map compiled at another scale or datum.^[1]

This page covers that connected water body and its immediate basin form. It does not assign the lake's 28,568 km² surface area to the much larger drainage basin, the Slave River Delta, the East Arm alone, or any administrative or protected area. The catchment reaches far beyond the Northwest Territories through the Peace and Athabasca headwaters even though the lake surface itself does not cross a territorial boundary.^[2][4]

The broad West Basin occupies the lake's western and southern part. The Slave River enters through its delta near Fort Resolution on the south shore, the Hay River enters near the southwestern town of the same name, and the lake narrows westward to the Mackenzie River outlet near Fort Providence. The North Arm extends toward Behchokǫ̀ and Yellowknife Bay. Eastward, an island-rich passage leads into the East Arm, whose northern McLeod Bay and southern Christie Bay are distinct deep-water basins.^[2][3]

This outline crosses a major rock boundary. Younger sedimentary layers of the Central Plains underlie the broad western lake, while ancient Precambrian rocks of the Canadian Shield frame much of the East Arm. The contrast appears both above and below water: low-relief shores and river-built sediment bodies dominate much of the west, whereas headlands, islands, narrow channels, and steep submerged rock slopes divide the east.^[2][3]

A whole-lake mean depth of 69 m conceals extreme compartmentalization. The West Basin averages about 41 m and reaches 163 m. The archipelago-like passage toward the East Arm reaches roughly 320 m but includes a sill—an underwater threshold—estimated near 100 m. Beyond it, McLeod Bay reaches about 293–300 m and Christie Bay descends to 614 m. The exact sill depth remains uncertain, so it should not be treated as a charted limiting depth.^[2][3]

Christie Bay's great depth is not explained by recent ice erosion alone. Its form follows faults associated with an approximately two-billion-year-old transform structure at the boundary between ancient crustal provinces. Later Laurentide glaciation reworked this inherited relief, eroded rock and sediment, and left deposits around the lowland margins. The modern lake therefore combines old tectonic control with much younger glacial modification.^[3]

During deglaciation, retreating Laurentide ice blocked northward drainage and parts of the present Great Bear, Great Slave, and Lake Athabasca basins were joined within glacial Lake McConnell. A published reconstruction places that changing ice-marginal lake between 11.8 and 8.3 thousand years before present and attributes its large extent mainly to glacial downwarping of the land.^[5]

As the ice load disappeared, the crust rose unevenly—a process called glacial isostatic rebound—and drainage gradients changed. The reconstruction places the final separation of Great Slave Lake and Lake Athabasca at about 8.3 thousand years before present. These dates describe phases of the wider proglacial lake, not a single excavation date or an exact “age” for today's shoreline.^[5]

A daily water-balance model for 1964–1998 found that about three-quarters of total input came through the Slave River from the Peace–Athabasca catchments, about one-fifth came from other basins bordering the lake, and 5% fell directly as precipitation. The Taltson, Lockhart, and Hay were the largest named contributors in the bordering-basin group. On the loss side, about 93–94% left through the Mackenzie River and 6–7% evaporated from the lake surface. These are period averages from a model that closed the annual balance to within ±6% in 28 of its 35 years; they are not fixed percentages for every year.^[4]

The lake delays and mixes that flow rather than simply passing it along one channel. The same study estimated a whole-lake residence time of 14.2 years for 1964–1998, with individual annual estimates from 10.4 to 19.7 years; the West Basin is expected to flush about twice as rapidly as the East Arm because it is shallower and much Slave River water follows the shorter route toward the outlet. “Residence time” is a volume-to-inflow replacement estimate, not the travel time of each parcel of water.^[4]

Lake level reflects the balance among river inflow, precipitation, evaporation, outflow, and changing storage. An ECCC/GNWT analysis of the exceptional 2020 high water used 28,568 km² as the surface area and warned that even a small stage error produces a large storage error; no bathymetry-based stage–volume curve was available for that analysis. Long-term variability is strongly linked to precipitation over the upstream Peace–Athabasca basins, while regulation of the Peace River has altered the seasonal timing of inflow.^[4][6]

The lake is seasonally ice covered and its surface layer is commonly described as dimictic: surface water passes through the temperature of maximum density near 4°C and can overturn in both spring and autumn. Depth changes that simple picture in Christie Bay. A 2019–2020 mooring showed seasonal mixing in roughly the upper 200 m, while water below about 186–200 m remained weakly but permanently stratified because pressure lowers the temperature at which freshwater is densest. This pressure-controlled effect is called thermobaric stratification.^[3]

Ice timing is not uniform across the lake or from year to year. At the Christie Bay mooring, ice began forming on 22 November 2019, full cover was reached on 7 December, and open water returned around 26 June 2020—201 days of complete cover at that location. Satellite observations in the study showed breakup earlier in the main lake, especially off the north-flowing Slave River, and later in McLeod Bay. Those dates are a documented one-year example, not a permanent lake-wide calendar.^[3]

Wind is most effective while open water permits direct transfer of energy to the lake. It mixes the shallower sectors, displaces internal density surfaces, and can drive lateral intrusions of cold water into deep Christie Bay. Once ice cover forms, wind forcing is cut off at the surface. Basin depth, the sill, inflow temperature, solar heating through spring ice, and autumn cooling therefore give the West Basin and East Arm different thermal responses.^[3]

Upstream, the Slave River connects Great Slave Lake to the Peace–Athabasca delta, Lake Athabasca, and headwaters in the northern plains and Rocky Mountains. Local tributaries drain both sedimentary lowlands and glaciated Shield terrain. Downstream, the Mackenzie River carries the combined flow north through the Mackenzie Valley to its delta on the Beaufort Sea.^[4]

Great Slave Lake sits on that main stem; Great Bear Lake instead joins the Mackenzie farther downstream through the Great Bear River. Within the atlas, the lake hub provides comparisons with other large through-flow basins, and the terrain index connects the lake's tectonic structure, glacial history, lowland sediment, and Shield relief.

1. Geographical Names Board of Canada, Great Slave Lake, Canadian Geographical Names Database key LAJNH, and the linked bilingual record Grand lac des Esclaves / Great Slave Lake (records modified 16 February 2021; accessed 30 August 2026). Sources for official names, lake classification, Northwest Territories location, and 61.500149° N, 114.001228° W map reference. The database identifies a polygon and assigns the coordinate 1:5,000,000 relevance; it is not presented here as a surveyed centroid.
2. Evans, M. S. and Muir, D. C. G., “Persistent organic contaminants in sediments and biota of Great Slave Lake, Canada: Slave River and long-range atmospheric source influences,” Journal of Great Lakes Research 42(2), 233–247 (2016; accessed 30 August 2026). The study's physical setting supplies the 28,568 km² area, 949,000 km² drainage area, 69 m whole-lake mean depth, 614 m maximum, 41/163 m West Basin mean/maximum depths, 199/614 m Christie Bay mean/maximum depths, approximately 120/293 m McLeod Bay mean/maximum depths, regional divisions, and Shield–sedimentary contrast.
3. Carmack, E. C. et al., “Thermobaric Processes Both Drive and Constrain Seasonal Ventilation in Deep Great Slave Lake, Canada,” Journal of Geophysical Research: Earth Surface 126, e2021JF006288 (2021; accessed 30 August 2026). Source for the 614 m Canadian Hydrographic Service chart-based Christie Bay maximum, West Basin and connecting-passage depths, uncertain sill estimate, bedrock boundary and approximately 2 Ga fault control, dimictic classification, 2019–2020 mooring methods, deep thermobaric stratification, and location-specific ice dates. The authors explicitly caution that their Christie Bay findings require further observations before being applied to the entire lake.
4. Gibson, J. J., Prowse, T. D. and Peters, D. L., “Hydroclimatic controls on water balance and water level variability in Great Slave Lake,” Hydrological Processes 20, 4155–4172 (2006; accessed 30 August 2026). Source for the functional daily water-balance model, its 1964–1998 period and closure errors, named local tributary shares, 14.2-year mean and 10.4–19.7-year annual residence estimates, contrasting basin flushing, and upstream precipitation and Peace River regulation controls. The abstract partitions input as 74/21/5% and losses as 94/6%, while the paper's long-term summary gives roughly 77/18/5% and 93/7%; because the reason for that internal difference is not stated, the prose uses “about three-quarters,” “about one-fifth,” and ranges for the loss terms.
5. Smith, D. G., “Glacial Lake McConnell: Paleogeography, age, duration, and associated river deltas, Mackenzie River basin, western Canada,” Quaternary Science Reviews 13(9–10), 829–843 (1994; accessed 30 August 2026). Source for the reconstructed 11.8–8.3 thousand-year-before-present glacial Lake McConnell sequence, its occupation of parts of the Great Bear, Great Slave, and Athabasca basins, glacial downwarping, and separation of Great Slave Lake and Lake Athabasca. Those dates describe the changing proglacial-lake system rather than a precise age for the modern shoreline.
6. Environment and Climate Change Canada and Government of the Northwest Territories, Hydrological Analysis for Great Slave Lake 2020: ECCC/GNWT Report on 2020 Water Levels (28 January 2021; accessed 30 August 2026). Source for the 28,568 km² modelling area, gauge network, residual-supply method, 2020 storage analysis, and the warning that a bathymetry-derived stage–volume relation was unavailable. This report says total volume is “over 1,070 km³,” whereas the morphometric source used by reference 2 reports 2,088 km³; because the boundary and calculation behind the difference are not established in the report, this page omits a single total-volume figure.