Pentad Lake

Drainage: Stillwater
Approaches: Approximately 25 miles round trip from the Box Canyon trailhead, with roughly 3,300 feet of climbing. All on trail.
Elevation: 9,394 feet
Fish: Yellowstone cutthroat, abundant and self-sustaining. Montana FWP.
Coordinates: 45.22433, -110.10127
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, over Columbine Pass, then downhill to Favonius and Pentad. Trail the whole way.

Pentad sits about half a mile northwest of Favonius. We came through in the middle of the afternoon and did not stop, headed for Sundown.

The hike

Pentad is 40.7 acres and 58 feet deep with a 24-foot average, which makes it the biggest and deepest water in this basin by a good margin.

Nobody knows where the fish came from. FWP's note says the origin is unknown and natural reproduction sustains the population, with some interaction with Favonius upstream. They sampled 25 cutthroat in 2022 by angling, averaging 10.9 inches and running up to 13.5, and 10 fish in 2016 at the same average. Their assessment was that the fish were in average shape.

Consistent size, no stocking record, and a self-sustaining population that has been there long enough that the state has stopped asking how.

There are plenty of campsites, though FWP says the firewood is a little picked over.

Tips & safety

• Navigation: On trail the whole way from Box Canyon over Columbine Pass, then down past Favonius.

• Camping: Plenty of sites. Firewood a little picked over.

• Fishing: Abundant self-sustaining cutthroat, consistently around 11 inches with fish to 13.5. FWP sampled it with a rod.

• Bugs: Mosquitoes, annoying rather than bad.