Just south of Ross Lake, Diablo Lake is held back by the 389ft Diablo Dam. A pullout off Hwy 20 known as the Diablo Dam Overlook provides incredible views of the turquoise-green lake framed by glacier-capped peaks.
Diablo was the world's highest arch-type dam at the time of its completion in 1930, and building it in such a hostile region with no road access is considered one of the greatest engineering feats of the interwar age. Diablo Lake is popular for kayaking and canoeing (there's a launch site at Colonial Creek campground). The water's turquoise hue is a result of powdered rock ground down by glaciers.