With its headwaters in the icefields on the western slopes of Mount Adams, the Lewis River flows westward through Gifford Pinchot National Forest to the western boundary of Skamania County. From there to the Columbia River, it represents the boundary between Cowlitz County and Lewis County. It is dammed along the way three times, by Swift Dam, by Yale Dam and by Merwin Dam. It passes through the small communities of Yale, Ariel and Cougar before crossing Interstate 5 at Woodland, near its confluence with the Columbia.
