Diablo Lake Overlook

Diablo Lake Overlook is a roadside viewpoint on State Route 20, looking down over a broad glacial reservoir ringed by steep Cascade peaks. The islands, long lake arms and Diablo Dam all fit into one open panorama, with the view right beside the road. I'd keep this stop on a Highway 20 drive; it gives you the big picture in a few minutes without taking the lakeshore trail. Walk along the overlook railing for a slightly different angle, and leave a few of the islands in your photo to show the lake's scale.

The milky green-blue color comes from glacial rock flour: tiny particles ground from bedrock and carried into the lake by meltwater. Green minerals in the local Skagit Gneiss give those particles their color, which mixes with the blue reflected by the water. For the strongest teal, aim for a sunny day in July, August or September. Cloud and weaker fall light can make the lake look more blue-gray, so the famous color isn't guaranteed.

Look across the reservoir for Diablo Dam, a 389-foot structure that created the lake. It was completed in 1930 and began generating electricity in 1936 as part of Seattle's Skagit hydroelectric project. From the overlook, the dam sits small against the mountains, which gives you a sense of the scale of the reservoir and the valley.

There's a roadcut across from the overlook parking area where pale igneous dikes slice through dark Skagit Gneiss. The gneiss formed under great heat and pressure; glaciers later carved the sharp peaks and ground rock that washes into the lake. It's a worthwhile second look if you want to understand why the water has its unusual color, not just take in the view.

The overlook is at mile 131.7 on State Route 20, and its wayside parking doesn't require a pass. The official amenities list includes auto and bus/RV parking, picnic tables and vault toilets. Tour buses and summer weekends can make the stop busy; an early weekday visit is a better bet for a quieter look. Highway 20 access can be seasonal, so check current road conditions before building your route around the lake.