The Duncan River is a 128-mile (206 km) long river in the Canadian province of British Columbia. Its drainage basin is 2,443 square kilometres (943 sq mi) in area. It is part of the Columbia River basin, being tributary via Kootenay Lake to the Kootenay River, which is a tributary of the Columbia River. It forms part of the boundary between the Selkirk Mountains, to its west, and the Purcell Mountains, to its east (the boundary northwards is the Beaver River).
|Source||near Mount Dawson|
|- location||Purcell Trench|
|Length||206 km (128 mi)|
|Basin size||2,443 km2 (943 sq mi)|
|- location||Below Lardeau River|
|- average||162 m3/s (5,700 cu ft/s)|
|- minimum||12.8 m3/s (450 cu ft/s)|
|- maximum||807 m3/s (28,500 cu ft/s)|
The Duncan River originates near Mount Dawson and flows south through the Purcell Trench between the Selkirk Mountains and Purcell Mountains. It flows into Duncan Lake, a natural lake that has been enlarged by Duncan Dam. A short distance below the dam, the Duncan River is joined by the Lardeau River, its largest single tributary. From here the river continues south to join the Kootenay River at the North Arm of Kootenay Lake.
On some early maps Duncan Lake is shown with the name "Upper Kootenay Lake" or "Howser Lake", but since 1912 the name Duncan has prevailed.
Before Duncan Dam was built the river served as the main navigation route into the valley, used by mining and logging industries. The route was navigable via Kootenay Lake as far as Bonner's Ferry, Idaho, on the Kootenai River.
Duncan Dam was finished in 1967, the first of the three Canadian Columbia River Treaty dams to be built. Its purpose is to regulate flow into Kootenay Lake, in coordination with Libby Dam, to assure sufficient water flow for the Kootenay Canal and Corra Linn Dam projects. Duncan Dam does not produce any electricity. Duncan Lake, originally 25 kilometres (16 mi) in length, is now 45 kilometres (28 mi) long.
- "Duncan River". BC Geographical Names.
- "The Rivers - Stories". Balance of Power. 2007. Archived from the original on November 6, 2011. Retrieved September 3, 2008.
- "Archived Hydrometric Data Search". Water Survey of Canada. Archived from the original on February 21, 2009. Retrieved October 19, 2008. Search for Station 08NH118 Duncan River below Lardeau River
- "Duncan Dam Project Water Use Plan" (PDF). BC Hydro. 2005. Retrieved September 3, 2008.[dead link]
- "Duncan Lake". BC Geographical Names.
- Duncan Dam Archived 2008-09-17 at the Wayback Machine, Touchstones Nelson, Museum of Art and History