Essentially every stream, except for the Firehole River (getting too warm, so give the fish a break), is worth a visit now. Fall River Basin streams continue to get cooling water coming from snow melting on the Madison and Pitchstone Plateaus. But mosquitos remain in huge numbers throughout the Basin. Evening PMD spinner falls and brown drakes make for excellent late in the day fishing on all these. During afternoon hours some emerging green drakes, down from their peak,remain here. On any of the Park meadow streams do not overlook presenting dry damsel patterns. On such as Slough,Boundary and Mountain Ash Creeks, Fall, Gibbon, Bechler, Yellowstone, Lewis, and Snake Rivers, these patterns can be very effective, but seem to be overlooked. Now that the meadow reaches on all these are drying out, terrestrial patterns should be in your fly box. And do not forget that ancient favorite, the humpy. It remains an excellent horsefly and deer fly pattern.