Fishing has been best in the mornings and slows down in the afternoons. This is because the water temperature rises and the fish shut down. Get there early and look for PMD's and caddis. Nymphing is good with flashback PT's and three dollar dips #16 and #18. Fish should start looking for terrestrials soon.
This river is fishing well, as this is a cold river and there are spruce moths starting to show up. It will be best where the big pine trees overhang the river.
Time for gulpers. The hatch of callibaetis starts at 9am and lasts until the wind blows. It seems to get windy at 11am every other day. Wind, please stop!!!
Yellowstone National Park
Slough Creek and Lamar River
These two rivers are now in great shape and fishing well. Morning hatches of PMD's #16, and caddis #14, #16. In the afternoons there are some drakes #12. In the evenings there are rusty spinners #16, and egg laying caddis #14, and #16. It is August and the terrestrials are starting, use small hoppers #10, #12, crickets #12, ants and beetles.
You won't catch many above the falls, but they will be big, meaning over 20". You need to be prepared to do lots of walking and actively look for a few fish. It is like a hunt and they could be feeding on just about anything. There are still lots of different things hatching; PMD's, caddis, drakes, goldens, and then there are hoppers, ants, and beetles. If you want more action, hike into the Black Canyon and fish big bushy dries. The fish won't' be as big, but you will get numbers.
The Gallatin is nice and cold and this is a good time of the year to fish it. Mornings you will have PMD's and caddis. In the afternoons there are flav's and drakes. There are small hoppers #10, #12 as well as ants and beetles.
Gibbon River and Gardner River
These two are great for action, fish the pocket water with stimulators, trudes, and wulffs. The fish run small, but they are active.
Madison River and Firehole River
August is the slowest fishing here, as the water is too hot, best to wait until September to fish these two rivers.
Lots of water, as the farmers are calling for it. Maybe that is good since it puts the fish on the banks. Not great for wading though. Early morning spinners, then PMD's and caddis. Afternoons are tough as not much is hatching at that time. In the evenings there are rusty spinners #16, and egg laying caddis #14, and #16. The box is easy to float and is nymphing well, try using rubber legs #6, and #8, and flashback droppers #16.
Reports are slowing down for numbers, but still some nice sized fish are being caught. As the weather gets warmer, look for the fish to move towards colder water like springs and tributaries. Best flies are mity mouse, henry's lake renegades #12, and #14, PT's #14, and #16, and olive crystal buggers #10.