One word pretty much summarizes the fishing report for the Henry's Fork...Salmonflies! However...I will warn you to continue reading this report at your own risk...
Even though adults are spread up and and down much of the river, that doesn't necessarily mean that trout will aggressively be slamming your dry fly patterns on every drift. You should still be able to find some hungry trout that can't refuse your offering, but chances are they will most likely already be full of nymphs if you're in the middle of the hatch.
With that being said, I'd say that the front of the hatch is working it's way past the Warm River confluence and should be in the Cardiac Canyon section any day now. There already has been adults spotted below lower Mesa Falls.
The Upper Henry’s Fork
Flows in the Box Canyon have been holding steady around 850 CFS.
There has been sporadic Salmonflies hatching below the Buffalo River confluence, but I'd predict that the front of the hatch should hit the The Box by this weekend or early next week as long as weather conditions stay favorable.
In the meantime, nymphing under an indicator with zebra midges in different colors is the most productive way to fish this section.
Harriman State Park opens to fishing on June 15th.
Warm River to Ashton
I floated this section on Saturday, and like I mentioned earlier, Salmonflies are in the air and many nymphs are still crawling their way onto the banks. Fishing started off slow in the morning, but definitely picked up once the air temperature increased. We found a few nice trout to commit fully in taking our dries, but had a dozen or so that would just come up and nose what we were using on top.
Be sure to also put a big rubberlegs nymph on as a dropper below your dry when hammering the banks.
We are very happy to report that work on the Ashton Dam has caused little affect on the water clarity. Flows are around 2,200 CFS which is average for this time of year.
I also floated from Vernon to Chester this past weekend and can report that this section is in the middle of the big bug hatch, which is maybe why the trout were not very interested in the thousands of adult Salmonflies that were floating down the river. We did manage to rise two large fish to our adult imitations, but can only imagine that most are full from the masses of nymphs that have made themselves available.
The stretch from the Ashton Dam to the Vernon Bridge is closed until the general fishing season opens on May 26th.
Reports are that Salmonflies have moved their way through Warm River so fish should be looking up and eager to fed on top.
Fall River is still a little off-color and very cold, so no migration of Salmonflies yet.
South Fork of the Snake
Flows are holding at 11,000 CFS and are predicted to remain at that level for an extended period of time. Water clarity is excellent, however still very cold. BWO have been hatching and don't be surprised if you see a Skwala stonefly or two. I fished a Skwala dry pattern a week ago and did surprisingly well against the banks and especially in the riffles.
However, subsurface fishing techniques will be the productive and yield the most fish.
All of the Madison is now open to fishing.
Reports are that the river is somewhat off color below Quake Lake and any tribuatary, but success is being had using early season nymph flies such as san juan worms and large rubberlegs.
In between the lakes has the best looking water but also the most crowds.
Henry's Lake is closed until the Saturday of Memorial Day Weekend.
Yellowstone National Park
Fishing is closed until May 26, 2012.