Cabin #1 is named for it, so we may as well explain. The salmonfly is a large stonefly — two inches of orange-bellied insect — and when it comes off the Yellowstone the whole river changes character for a couple of weeks.
Roughly when
The hatch generally runs from late June into July, but the date is not the useful part. Salmonflies emerge as water temperatures climb after runoff, so the hatch moves upstream through the valley over a week or two rather than switching on everywhere at once. A cold, heavy runoff pushes everything later; a mild spring pulls it forward.
What we watch is water temperature. Once the river reaches about 54 degrees, the hatch is close. The local fly shops all post fishing reports, and they are the easiest way to know when the bugs are showing up in a given year.
What it looks like
Look for the empty nymphal shucks on streamside rocks and willows. They are a sure sign the hatch is on. But the best fishing is usually just ahead of the main hatch, when the trout have started keying on the big bugs and before they have eaten so many that they are gorged and stop feeding. If the shucks are everywhere where you are standing, the best of it may already be a few miles upstream.
How to fish it
The best dry-fly fishing with adult salmonflies tends to be in the evening. Before the adults start emerging, though, some of the best fishing of the year is with nymphs near the bank. A Pat's Rubber Legs is the standard. The nymphs crawl toward shore to climb out of the water and hatch into adults, and the trout feed on them along the way.
If you miss it
The valley does not run out of insects. Caddis, mayflies, hoppers through late summer, and the skwala early in spring — which is to say four more of our cabins are named after your backup plan.
The river is a couple of minutes' drive from the cabins. Ask us what we are hearing before you head out.