- Diablo Lake is a teal gem nestled in the Cascades. Travelers on State Route 20 often stop at the Diablo Lake overlook to marvel at the lake’s vivid hue. Diablo Lake is used as a reservoir, created by the Diablo Dam. It is one of three lakes in the area used for power generation, along with Ross Lake to the north and Gorge Lake to the south. Seattle City Light manages the power generation as part of the Skagit River Hydroelectric Project. The lake is a popular place to kayak or canoe, but be prepared for a chilly swim should the boat tip over; the water temperature of lakes in this area rarely exceeds 50°F, even in summer. This stop is more than just a place to stretch your legs. It is a world of quintessential Cascade vistas of rock spires and snowfields set against a multitude of striking greens and blues. You won’t be disappointed.