The Firehole River is now warm enough that you do its trout a favor by fishing elsewhere. Brown drake hatches are done for the year on Duck Creek and the Gibbon River meadow reaches. Concentrate on presenting terrestrial patterns for better dry fly fishing on these. Slough Creek is fishing well through presenting terrestrial patterns (but hosts almost as many fly-fishers as fish). Also concentrate on presenting these on Bechler River and Boundary Creek. Yellowstone River is now open to fishing above the falls. Big stoneflies are about to go through. Fishing on Shoshone Lake tapers off this time of year, but picks up in September, same with Lewis Lake. If you intend to fish Fall River in the park, water releases from Grassy Lake much impact fishing success this time of year. These releases happen on irrigation demand, and can be irregular well into August. For a few days after such a release wet fly fishing (streamers, wooly bugger types, SJ worms, etc.) beats dry fly fishing if you want to encounter the large cut-bows present in the river.