Cosley Lake

Overview

Cosley Lake sits deep in the Belly River/Mokowanis country, a quiet corner that feels like Glacier before the crowds. Expect a true backcountry vibe—big peaks, blue water lined with red stones, and the kind of stillness that makes camp chores feel like a privilege.

How to Get There

• Belly River route: About 20.6 miles out-and-back with roughly 1,968 feet of gain from the trailhead near the U.S.–Canada border. The path rolls through meadows and aspen stands, with spurs to Gros Ventre Falls and on toward Glenns Lake.
• Many Glacier via Ptarmigan Tunnel: A spectacular but tougher linkup, listed around 27.4 miles out-and-back with about 5,846 feet of gain. You’ll pass Ptarmigan Falls and Ptarmigan Lake, go through the tunnel, drop past Elizabeth Lake, and continue to Cosley.

Camp Life

Cosley Lake’s backcountry campground is small and civilized by Glacier standards: four roomy sites, a pit toilet, a shared food-prep/hang setup, and quick access to the shore. It pairs nicely with Elizabeth Lake (Foot) if you’re stitching together a 2–3 day trip. Backcountry permits are required.

Scenery & Side Trips

Make time for the waterfall detours. Gros Ventre Falls is an easy add-on from the Belly River approach, while Dawn Mist Falls near Elizabeth Lake is a thundering highlight from the tunnel route. Around camp, the lake’s color and stone-studded shoreline are the stars.

Wildlife

This valley sees regular moose traffic near camp and on the flats, and birders often note common loons (with nearby sightings of swans and cranes). It’s also grizzly country—carry spray, store food properly, and give all wildlife generous space.

Conditions to Expect

Weather changes fast, especially near the tunnel and passes—pack insulation and rain layers even on bluebird mornings. Early season can bring mosquitoes; late season may mean pulled footbridges and chilly fords. Cell coverage is unreliable; download maps and navigate accordingly.

Best Time to Visit

Trails are generally in shape from May through October, but July–September is the sweet spot for firm tread and installed bridges. If you’re taking the Ptarmigan Tunnel route, verify tunnel status before committing.

Who It’s For

Backpackers who want Glacier’s wild side without front-country bustle. If you’re looking for a quick roadside lake, this isn’t it. If you’re up for miles and want waterfalls, wildlife, and a serene camp, Cosley is a gem.