Mouse Lake

Drainage: Stillwater
Approaches: Approximately 27 miles round trip from the Box Canyon trailhead, with roughly 3,650 feet of climbing. The last mile is off trail.
Elevation: 9,581 feet
Fish: Yellowstone cutthroat, abundant, stocked with some natural reproduction. Montana FWP.
Coordinates: 45.20954, -110.09527
Bugs: Mosquitoes, just bad enough to be annoying.

Getting there

Trail #27 up the East Fork of the Boulder past Lake Kathleen and Lake Columbine, then up to Columbine Pass. The trail carries on past the pass to Favonius. Mouse is the one you leave it for.

We came at it from a camp at Columbine. The pass is an hour and forty minutes above the lake, and our track put the high point at 9,890 feet. It is a nice climb through green meadow full of flowers, and it is the prettiest part of the day.

From the pass we went off trail and dropped to Mouse, another forty-five minutes. Two and a half hours from camp.

FWP describes the same line: over Columbine Pass, then around the unnamed lake to the east and southeast.

The hike

Mouse is 6.9 acres, 30 feet at the deepest and 13 on average.

The cutthroat here are worth the walk. FWP sampled 33 fish in 2022 averaging 13.6 inches with the biggest at 16.9, and 11 in 2016 averaging 13.9. They took that 2022 sample with nets and a rod both. Their note is that the fish were ripe and appeared to be spawning on the shoreline gravel, which is why they class the population as stocked with some natural reproduction going on. It gets 345 fish every eight years, most recently in 2024.

There are flat spots near the lake with firewood, though FWP calls them rocky.

Tips & safety

• Navigation: On trail to Columbine Pass, off trail after. FWP's line from the pass is around the unnamed lake to the east, then southeast.

• Camping: Flat areas near the lake with firewood, rocky ground.

• Fishing: Abundant cutthroat running 13 to 14 inches with fish to nearly 17. FWP caught them on a rod as well as in nets.

• Bugs: Mosquitoes, annoying rather than bad.

• Columbine Pass: Green meadow and flowers, and the best walking of the day.