Horseshoe Lake (Upsidedown Creek)

Drainage: Boulder
Approaches: Approximately 15 miles round trip on Upsidedown Creek Trail #26, with roughly 3,390 feet of climbing. All on trail.
Elevation: 9,587 feet
Fish: Yellowstone cutthroat, common and self-sustaining. Montana FWP.
Coordinates: 45.26847, -110.18172
Bugs: Mosquitoes, just bad enough to be annoying.

Getting there

This is the first lake you come to on the Upsidedown Creek Trail, seven and a half miles in and all of it on trail. FWP calls the trail steep but very well maintained, and says the lake receives heavy use — being the first water on a good trail will do that.

We came at it going the other way, walking out on the last morning of a nine-day traverse, and reached it a bit after eleven.

The hike

Horseshoe is a wide shallow spot in the creek. It is 15.9 acres but only 10 feet at the deepest and 4 on average, and FWP flags it as having potential to winterkill.

The recent numbers suggest that is not theoretical. In 2015 they sampled 12 cutthroat averaging 11.4 inches with fish to 13.9. In 2025 they got 14 averaging 7.7, with the biggest at 10.7. Same lake, ten years apart, and the fish are markedly smaller.

The population is self-sustaining regardless — the only stocking on record is 291 fish in 1970.

FWP says the camping is good but the firewood is picked over, which follows from the traffic.

Tips & safety

• Navigation: On trail the whole way. First lake on the Upsidedown Creek Trail.

• Camping: Good, but firewood picked over. Expect company.

• Fishing: Self-sustaining cutthroat, running smaller than they used to. FWP flags winterkill potential in a lake this shallow.

• Bugs: Mosquitoes, annoying rather than bad.