The Similkameen River runs through southern British Columbia, Canada, eventually discharging into the Okanagan River near Oroville, Washington, in the United States. Through the Okanagan River, it drains to the Columbia River. The river is said to be named for an indigenous people called Similkameigh, meaning "treacherous waters".

The river is controversially dammed (the now-defunct Enloe Dam), blocking fish passage to the upper (Canadian) reaches of the river.

The first mention of the Similkameen by a European was by Alexander Ross. While on a trading expedition, he travelled by way of the "Similkameigh River." Sir George Simpson used the name "Similkameigh" for one of the groups part of the Okanagan Nation. The transition from Similkameigh to Similkameen may have been inspired by the name of the Tulameen River despite being etymologically incorrect. The name Similkameigh comes from a now-extinct language of Nicola-Similkameen, of the Athapascan languages, and is believed to mean "Salmon River."

It starts at Nordheim Peak, on the east flank of Manning Park, about 10.3 km (6.4 mi) north of Allison Pass and flows past the settlements of East Gate, Princeton, Hedley, Keremeos, and Cawston, closely followed by Highway 3, the Crowsnest Highway. About 25 km (16 mi) upstream from Princeton, the river drops over Similkameen Falls. Numerous viewpoints of the river occur from the highway, the most popular being Bromley Rock, where swimming in the river from a spectacular sandy beach is possible. In a typical Okanagan, BC summer, the water is warm and fantastic for swimming. 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 m/s), with a recorded maximum of 45,800 cu ft/s (1,300 m/s) and minimum of 65 cu ft/s (1.8 m/s).

The Enloe Dam, completed in 1920, is located just above the river's mouth. The river, after flowing over the dam, drops over what is left of Coyote Falls. Lacking fish ladders, Enloe Dam blocks fish passage and completely extirpated anadromous fish migration into the upper reaches of the Similkameen River and its tributaries in Canada. However, Coyote Falls is 20 feet tall thus making it impossible for salmon (who can only jump 12 feet) to migrate further than that point and would never reach the dam.

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 west of Keremeos

• List of rivers of British Columbia
• List of rivers of Washington (state)

48°53′30″N 119°25′49″W / 48.89167°N 119.43028°W / 48.89167; -119.43028