I have made 10-12 trips to Slough Creek over the years and have never had a bad day of fishing there. Slough Creek is divided into four primary sections, the lower meadow and the second, third and fourth meadow. The road access is to the lower meadow and the three upper meadows can be reached via the Slough Creek Trailhead. The second meadow is the only one of the 3 upper meadows that is practical to fish without having to camp but is a bit of a hike from the trailhead. Due to time constraints, I have only been to the second meadow twice and it was worth the hike. Aside from the plentiful and large Cutthroats, this area is one of the best wildlife areas in the whole Park. I saw my first Grizzly bear here, got charged by a buffalo and have caught numerous Cutthroats over 20". There is no wonder that Slough Creek has had so many articles written about it over the years. In my opinion, it is almost exclusively a dry fly stream. Between meadows there are faster stretches where a nymph might work but the meadows are, for the most part slow moving and perfect for a dry fly. Terrestrials, especially a #16 black beetle have been my most successful flies.
Fly Fishing Slough Creek - by Fly Fishing Yellowstone National Park
Slough Creek - by Montana Angler
Yellowstone Slough Creek Fly Fishing 2014 - video by Dina Dexheimer