[5] The earliest known mention of the river name was 1889[6] in honour of John (Jack) Duncan, a prospector and candidate for the colonial Legislative Council from the Kootenay Land District in 1866.

[12] Thousands of years ago, prior to reclamation by silting, the present mouth of Meadow Creek (about 10 kilometres (6 mi) up the Duncan River) was part of Kootenay Lake.

[13] By the early 1890s, various small craft were travelling northward between the timbered slopes bordering the turbulent, log-jammed river.

[17] That summer, the Idaho carried prospectors and supplies on regular 32-kilometre (20 mi) runs into the upper river as far as a log jam.

[18] After leaving Duncan City, the Idaho would travel about 11 kilometres (7 mi) north to Jubilee Point on the east shore, the headquarters of the Gold Hill Exploration and Development Co.[19][20] The Matthews ranch was also on the peninsular.

In later decades, only the flagpole and rock fireplaces remained of the abandoned assay facilities, prior to flooding by the Duncan Dam reservoir, which changed the peninsular into an island.

[22] Since 1896, the federal government had been clearing the lower river of obstructions to make it navigable for eight months of the year.

[28] Once the railway was built, the lower river was no longer kept clear by the government and became unnavigable for larger vessels.

[17] The upper river was kept clear but was only navigable by small boats from May to early September,[30] when the water was sufficiently high.

[32] The forestry phone line, which was attached to trees, followed the east shore of the lake and river to McGuire Creek and then terminated at Healy.

[34] At the time, people lobbied for a road from the foot of the lake up the east side of the river to Healy's Landing, where a trail extended to Hall Creek.

[36] Although forest, wildlife habitat, and homes on lower ground were submerged, the reservoir became popular for fishing and boating.

[27] The trestle pilings over Limey's Slough on the abandoned grade about 2 kilometres (1.2 mi) northeast of Marblehead remained until the dam was built.

[48] Starting from Lardeau, CP finally laid track, reaching the second crossing at Gold Hill that November.

[57] The dam extended the lake about 5 kilometres (3 mi) southward, submerging largely an area of sloughs.

[62] Lake tributaries include Griz,[63] North, Gallop, Little Glacier,[64] Howser, Idaho, Maude, Labarie, and Tiger creeks (but the latter five are upper river at low water).

[73][74] The first bridge across the river was near Cooper Creek[75] (about 2.7 kilometres (1.7 mi) from the Duncan mouth), which existed until the mid-1920s.

[81] A week later, the spring high water carried log debris, which pounded the bridge pilings.

[83] In 1964, a loaded logging truck collapsed this bridge, which was replaced by a two-span 55-metre (180 ft) crossing that December.