Ross Lake stretches across 23 miles north toward the Canadian border. In keeping with the wild terrain, it's accessible only by trail or water. Part of the Ross Lake National Recreation Area, the lake formed as a result of the Ross Dam, an ambitious hydroelectric project from 1937 that was designed to generate electricity for the fast-growing Seattle area.
You can hike down to the Ross Dam from a trailhead on Hwy 20. The trail descends for 1 mile and crosses over the dam.