The Similkameen River runs through southern British Columbia, Canada, eventually discharging into the Okanogan River near Oroville, Washington in the United States. The river is approximately 197 kilometres (122 mi) long, with a drainage basin area of 7,600 square kilometres (2,900 sq mi). The river is said to be named for an indigenous people called <Similkameigh>, meaning "treacherous waters".
It starts on the east flank of Manning Park, about 10.3 kilometres (6.4 mi) north of Allison Pass and flows past the settlements of Eastgate, Princeton, Hedley, Keremeos, and Cawston, closely followed by Highway 3, the Crowsnest Highway. About 25 km upstream from Princeton the river drops over Similkameen Falls. There are numerous viewpoints of the river from the highway, the most popular being Bromley Rock, where it is possible to swim in the river from a spectacular sandy beach, although the water is very cold. It contributes 75% of the flow of the Okanogan River and crosses the international border at Nighthawk, Washington.
The United States Geological Survey maintains a stream gauge at river mile 15.8, just upstream from the Oroville—Tonasket Irrigation District canal intake. The river's discharge (flow) at this point averages 2,283 cubic feet per second (64.6 m3/s), with a recorded maximum of 45,800 cubic feet per second (1,300 m3/s) and minimum of 65 cubic feet per second (1.8 m3/s).
The Similkameen River subject to international water-sharing agreements governed by the International Joint Commission as part of the Columbia Basin. The authority responsible for overseeing the IJC agreements is the International Osoyoos Lake Board of Control, composed of appointees from Environment Canada, the BC Ministry of Water, Land Air Protection, the US Army Corps of Engineers, the US Geological Survey, and private consultants.
- Pasayten River: Confluence is just above Similkameen Falls
- Tulameen River: Enters at Princeton
- Ashnola River: Meets the river 11 km east of Keremeos
- U.S. Geological Survey Geographic Names Information System: Similkameen River
- "Similkameen River". BC Geographical Names.
- Okanogan Subbasin Plan, Northwest Power and Conservation Council
- Bright, William (2004). Native American placenames of the United States. University of Oklahoma Press. p. 444. ISBN 978-0-8061-3598-4. Retrieved 14 April 2011.
- "Water resources data for the United States, Water Year 2010; gage 12442500, Similkameen River near Nighthawk, WA" (PDF). USGS. Retrieved 14 April 2011.
- Annual Report to the International Joint Commission from the International Osoyoos Lake Board of Control, 2004
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