Horn River formed along the middle course of the Horn River, and is followed downstream by the "Second Lake". The river turns south-west, where the "Mink Lake" is formed along its course. The Laferte River also flows into the Mink Lake. Horn River then flows south, and it receives the waters of the Bluefish River before it empties into the Mackenzie River, downstream from the Great Slave Lake), immediately upstream from Mills Lake, at an elevation of . The arch made by the river defines the "Horn Plateau", a flat elevated area that rises up to ) to the north and east,
Lake Athabasca depth of , and holds of water, making it the largest and deepest lake in both Alberta and Saskatchewan, and the eighth largest in Canada. Water flows northward from the lake via the Slave River and Mackenzie River systems, eventually reaching the Arctic Ocean. Fort Chipewyan, one of the oldest European settlements in Alberta, is located on the western shore of the lake, where the Rivière des Rochers drains the lake and flows toward Slave River, beginning its northward journey along the eastern boundary of Wood Buffalo National Park. The eastern section of the lake narrows to a width of