Place · 0.8 mi away
Overview
Lake McArthur is a high-alpine stunner tucked between Mount Schaffer and Park Mountain. Think saturated sapphire-blue water set in a stark limestone bowl, far from road noise and day-hiker crowds. It’s a classic O’Hara-area payoff: big scenery, intimate shoreline, and a sense of seclusion once you reach it.
What You'll See
Expect a long, cobalt lake (about 1.5 km) backed by rock walls and lingering snowfields. On calm days, you’ll get mirror reflections; when the wind kicks up, the surface can turn choppy fast. Summer brings bursts of alpine wildflowers on the approach, and fall lights up the larches—photographers love both seasons.
Geology and Hydrology
McArthur sits in a karst limestone basin with no visible outlet—the water drains underground through fractures in the rock. Its great depth (about 85 m—the deepest in the park) and clarity drive that signature deep-blue color.
Access and Regulations
Getting here isn’t casual. The entire Lake O’Hara area is tightly managed to protect its fragile alpine environment, so you’ll need advance reservations for the shuttle or the campground. The McArthur Valley is closed from May 1 to August 15 for grizzly bear protection; after August 15, access remains limited by permit. Plan ahead or pick another objective.
The Hike
Trails start near the Le Relais Day Shelter in the O’Hara area. You can reach McArthur via two options:
- High Level Circuit: more challenging with minor scrambling and airy traverses.
- Low Level Circuit: the easier, no-scramble option most hikers prefer.
Allow a half day overall; route choice and photo stops will dictate your time.
Wildlife
This corridor is busy with wildlife. Grizzly activity is the reason for those seasonal closures. Keep your eyes and ears open for marmots and pikas in the talus, and the occasional mountain goat on nearby slopes.
On-Site Amenities
None. No restrooms, no picnic tables, no potable water, no services—just a shoreline boulder for lunch. Everything you need, you carry in and out.
Best Time to Visit
Late August through September is prime: closures have eased, crowds thin compared to the O’Hara core, and larches turn. For photography, mornings often bring calmer water and softer light; weekdays are quieter than weekends. Weather can change quickly at this elevation—pack layers even in mid-summer.
Pros
- Deepest lake in the park with striking sapphire-blue water
- Quieter than the busy Lake O’Hara core trails
Cons
- Access is strictly controlled and requires hard-to-get reservations
- Seasonal closures for grizzlies limit access May 1–Aug 15
Tips
- Book Lake O’Hara shuttle or campground reservations well in advance.
- Confirm McArthur Valley closures and permit limits before you go.
- Choose the Low Level Circuit if you want to avoid scrambling and exposure.
- Carry bear spray and know how to use it—this is an active wildlife corridor.
- Start early for calmer water, better light, and fewer people at the shore.
