It starts on the east flank of Manning Park, about 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 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.