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The North Cascades Highway didn’t open until June 14 this year — the latest start to the season since 1974, after a December washout tore out entire sections of pavement along State Route 20.
That’s bad news if you wanted an early-season drive. It’s very good news for anyone heading up now, because Diablo Lake’s glacier-fed water is hitting peak turquoise right as the road finally lets you in.
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Why this year’s opening was so late
Crews spent the spring rebuilding sections of SR-20 between the Ross Dam Trailhead and Porcupine Creek, where the road had washed out and the remaining pavement was left unsupported underneath. WSDOT beat its own midsummer estimate and reopened both lanes on June 14 — over a month past the highway’s typical late-April or May opening.
The road still closes every winter regardless, usually by late November once snow and avalanche danger take over the high stretch near Washington Pass. This year’s late start was the exception, not a new normal.
Why the lake looks photoshopped
Diablo Lake’s color comes from glacial flour — fine rock particles ground up by the Neve and Colonial Glaciers and carried into the lake through meltwater streams. The particles are so small they stay suspended near the surface, reflecting green light back at you while the water underneath does what water normally does with blue.
The effect builds through summer as glacial melt ramps up, and it peaks on sunny days between July and September. Show up in April and you’ll see a nice lake. Show up right now and you’ll see something that looks fake in photos.
How to actually see it
Diablo Lake Overlook is the easy option — a paved, quarter-mile stretch right off SR-20 with picnic tables, restrooms, and a view that requires zero physical effort. No entrance fee, no permit, just a pull-off.
For a bit more payoff, Thunder Knob Trail starts across from Colonial Creek Campground and climbs 669 feet over 3.3 miles round trip to a knob with one of the best angles on the lake in the whole park. It gets hot and crowded by midday in summer, so mornings are your friend.
If you’d rather sit than hike, Skagit Tours runs a glass-roofed boat, the Alice Ross IV, out onto the lake from July 3 through early September. It’s the easiest way to get out on the water without your own kayak or paddleboard, and bookings go through the North Cascades Institute.
Getting there
Diablo Lake Overlook sits about three hours from Seattle via I-5 and SR-20, eleven miles east of Newhalem. With both lanes finally open, it’s back to being a straightforward drive instead of a construction-zone gamble.
Colonial Creek Campground sits right at the Thunder Knob trailhead if you want to make it a weekend, and there are a dozen more North Cascades trails worth the detour once you’re already out that way.
Trip tips: grab a rental car to make the drive out, lock in your hotel before the good rooms are gone, or skip both and book a camper van instead and post up at Colonial Creek.
Which are you doing first — the overlook, the hike, or the boat?
Rules and fees change — always confirm current requirements before you go.
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