Henry's Fork Report - August 15, 2024

Henry’s Fork Streamflows

Island Park Dam:  790 cfs

Ashton Dam:  1630 cfs

St. Anthony:  1120 cfs

Fall River:  382 cfs

Mid August in Henry’s Fork country brings about a river that is incrementally decreasing in flow, generally dropping in temperature due to longer nights and cooler weather, and increasing slightly in turbidity.  We expect to see fishing activity get better slowly over the next weeks, as the lower water temperatures of late summer begin to take hold.  Flows will decrease and the river will be more responsive to changes in temperature and weather.  Weeds will be on the increase, anglers should find a way to efficiently deal with them.  Look for periods of good fishing activity and be prepared to pivot with changing weather conditions in location or technique to find success.

Box Canyon

At 790 cfs, the Box is a great mid-August float, it’s still high enough to spend just a short morning, afternoon or evening in there and low enough to spend a full day working its waters slowly and carefully.  Weed growth is high but normal for the season, with decreasing flows anglers will do well to check their flies often to make sure they’re clear of any shrubbery.  Indicator nymphing is the primary choice here, but a streamer run isn’t out of the question.  6’ from indicator to fly with a BB or B split shot will put you in the game in the fishy water, lose the split shot in the shallows to hunt for straggling trout in the shallow flats.  For nymphs, we are generally throwing rubberlegs, 101 stones, SJWs, and leech patterns #6-10, smaller mayfly nymphs like a PT, Tactical R/L PT, Split Back PMD #16-18, caddis like a Hare and Copper, HP Caddis Pupa and Shop Vac #14-18, Red and Brown Zebra Midges #14-16, and Black Zebra Midges #18.  Perdigon style nymphs are useful as well:  Spanish Bullet, Bullet Quill, Olive Hot Spot, Jig Napoleons in Red and Yellow, Frenchies #14-18.  For streamers, we like Copper Zonkers, Black and Olive Bouface Leeches, and BFEs in Olive/Black, Black, and White.

Railroad Ranch

Despite small glimmers of hope in the last weeks, the fishing on the Ranch has been pretty tough overall with fewer and more difficult trout in the past weeks.  We at Big Sky Anglers are plagued by the eternal optimism that defines all anglers and we hope to see an overall increase in activity this week.  That said, we don’t expect things to drastically change out there, rather to incrementally improve over the coming weeks.  Each day will be a different day than the one prior and the one to follow, so being prepared for any one of a number of situations will favor the Ranch angler this week.  Mornings’ hope is for small mayfly spinners, followed by honey ants or small black flying ants.  Afternoons might yield anything from callibaetis spinners, grasshoppers, or PMD hatches to small caddis.   Patterns we like at the moment are:  Copenhaver Spinners and Harrops Paraspinner in both rusty, trico and pmd #16-20, Callibaetis spinners #14,  HF Caddis olive #16-18, Heames and Harrops Honey Ants #14-16, Shimazaki CDC Ant #18-10, Halfback #14-18, Last Chance Cripples PMD and baetis #16-20, Gray Drake Spinners and Duns #12, Moorish Hoppers and other varietals #4-8.  Hot, sunny afternoons will favor terrestrials, stormy ones will favor PMDs, baetis, and caddis. 

Canyon Country

The canyons of the Henry’s Fork continue to provide an action-packed day of rafting and flyfishing fun with decent action on smaller trout and the occasional larger surprise.  Chubberlegs rigs are a solid choice, change out the rubberlegs nymph for a size 12-14 perdigon for more action if things are slow.  These wilderness sections are a great way to spend a summer day.  Rafts are highly recommended, if not required, and solid oarsmanship a must.

Warm River to Ashton

This piece of water makes for a fun late summer float, there is opportunity to fish a number of different techniques successfully with a “risk vs. reward” mentality.  Streamers and large dry flies will produce fewer but larger trout while nymphing rigs will provide more steady action on smaller trout.  There’s a little “Choose Your Own Adventure” going on down here at the moment, and anglers will find decent days of angling in this reach.  Fly selections for the Box Canyon will be appropriate here as well.

Below Ashton Dam

Mornings will provide some sparse but quality activity, anglers should keep an eye on water temperatures in the lower reaches of the Henry’s Fork.  After the clock strikes noon on a sunny day, anglers should be ready to pivot to lower water temps and higher elevations.