MACKENZIE  , a

river of the North-West Territories, Canada, discharging the waters of the Great Slave Lake into the Arctic Ocean . It was discovered and first navigated by Sir Alexander Mackenzie in 1789 . It has an average width of 1 m., an average fall of 6 in. to the mile; an approximate discharge, at a medium stage, of 500,000 cub. ft. per second; and a total length, including its great tributary the Peace, of 2,350 M . The latter rises, under the name of the Finlay, in the mountains of British Columbia, and flows north-east and then south-east in the great intermontane valley that bounds the Rocky Mountains on the west, to its confluence with the Parsnip . From the confluence the waters of the combined rivers, now called the Peace, flow east through the Rocky Mountains, and then north-east to unite with the river which discharges the waters of Lake Athabasca; thence to Great Slave Lake it is known as Slave river . Excluding the rivers which enter these lakes, the principal tributaries of the Peace are: Omineca, Nation, Parsnip, Halfway, North Pine, South Pine, Smoky, Battle, and Loon rivers; those of the Mackenzie are the Liard (65o m. long), which rises near the sources of the Pelly, west of the Rocky Mountains, and breaks through that range on its way to join the parent stream, Great Bear river, which drains Great Bear Lake, Nahanni . Dahadinni, Arctic Red, and Peel rivers . The Mackenzie enters the Arctic Ocean near 135° W. and 68° 5o' W., after flowing for 70 to 8o m. through a flat delta, not yet fully surveyed . With its continuation, Slave river, it is navigable from the Arctic Ocean to Fort Smith, a distance of over 1,200 m., and between the latter and the head of Lesser Slave Lake, a further distance of 625 m., there is only one obstruction to navigation, the Grand Rapids near Fort McMurray on the Athabasca river . The Peace is navigable from its junction with Slave river for about 220 M. to Vermilion Falls . The Mackenzie is navigable from about the loth of June to the loth of October, and Great Slave Lake from about the 1st of July to the end of October . All the waters and lakes of this great system are abundantly stocked with fish, chiefly white fish and trout, the latter attaining to remarkable size .