Diablo Lake
State Route 20
Newhalem, WA
A reservoir the color of a tropical lagoon, glowing turquoise beneath the raw, glaciated peaks of the American Alps.
Diablo Lake stops people in their tracks. The water is a luminous milky turquoise, the color you expect from a Caribbean bay, not a mountain reservoir sitting under snow-streaked granite peaks. From the overlook on the North Cascades Highway, the lake glows against a backdrop of some of the most rugged mountains in the Lower 48.
The color is pure geology, and the lake itself is a piece of engineering history: one of three reservoirs on the upper Skagit River built by Seattle City Light to power a distant city. The result is a place where wild alpine scenery and early twentieth-century ambition sit side by side.
What Guests Love
- The unreal turquoise color of the water, especially from the Diablo Lake Overlook on Highway 20
- Jagged, glacier-hung peaks like Colonial and Pyramid rising straight from the shore
- The story of the Skagit dams and the little powerhouse towns that built them
- Kayaking or taking a boat tour across water that looks lit from below
Worth Knowing
- The North Cascades Highway over the pass closes in winter, so the overlook and upper lake are a late-spring-to-fall visit
- The turquoise is most vivid in summer, when glacial melt is running; it fades toward a darker green in cooler months
- The lake is a cold, deep reservoir with fluctuating levels, and it is genuinely frigid for swimming
- This is remote country with few services; fuel and supplies up in advance
Details
Newhalem, WA
Learn about Diablo Lake
Why the water glows
The turquoise comes from what geologists call rock flour, or glacial flour. As glaciers grind slowly over bedrock, they pulverize rock into a powder so fine it stays suspended in the meltwater rather than sinking.
When that cloudy, mineral-rich water fills the lake, the tiny particles scatter sunlight, reflecting back the blues and greens and giving Diablo its glowing, opaque color. The effect is strongest in high summer, when the glaciers above are melting hardest and feeding the most flour into the water. Cooler seasons slow the melt, and the color deepens and dulls.
The dams that made the lake
Diablo Lake is a reservoir, held back by Diablo Dam, one of three Seattle City Light dams on the upper Skagit, along with Gorge and Ross. They were driven in the 1920s and 1930s largely by a determined utility superintendent, J. D. Ross, to bring hydroelectric power to Seattle far to the west.
When Diablo Dam was finished it was briefly among the tallest in the world. To build and run the dams, the utility raised the small towns of Newhalem and Diablo in the wilderness, complete with housing and a landscaped garden, and for decades ran popular tours up an incline railway. The dams still generate a large share of Seattle's power today.
The American Alps
The peaks around Diablo are why the North Cascades earned the nickname the American Alps. This is some of the steepest, most heavily glaciated terrain in the country outside Alaska, with hundreds of small glaciers clinging to the high walls.
Colonial Peak and Pyramid Peak loom over the lake, and trails like Sourdough Mountain and Thunder Knob climb into the surrounding North Cascades National Park complex. Much of this landscape is protected wilderness, so the scenery from the highway is only a hint of the country behind it.
Wildlife and seasons
The valleys here are prime habitat, part of one of the wildest corridors in the Lower 48. Black bears are common, and the range still holds rarer animals higher up. Watch the ridges for mountain goats and the sky for eagles over the water.
The high country is a warm-season destination. The North Cascades Highway over Washington and Rainy Passes closes under deep snow each winter and reopens in spring, so plan a Diablo Lake trip for roughly late spring through October, when the color and the peaks are at their best.
Closest Boutels
The closest Boutel™ stays, so you can turn this stop into an overnight. Each is an independently owned, editorially selected place to stay.
Things to Do Near Newhalem
North Cascades Visitor Center
About 6 miles west, in Newhalem
The main visitor center for the national park complex, with exhibits on the range's geology and ecology and short trails into old-growth forest.
Washington Pass Overlook
About 30 miles east
A short paved path to a jaw-dropping view of Liberty Bell and the highway switchbacking through the high North Cascades.
Ross Lake
Just upstream
The largest of the Skagit reservoirs, a long fjord-like lake stretching north toward Canada, reached by trail, water taxi, or a gravel road from British Columbia.