Henry’s Fork

Henry’s Fork, June 26th, 2024

Here is some great info from Dr. Rob Van Kirk’s Henry’s Fork Watershed SWE report filed June 25^th. Hatch timing is accelerating again after slowing down for a few days early last week and is near average at most locations. Green Drakes are slowing down on the lower river (downstream of Warm River) but are hatching upstream. A few flavs have been seen on the lower river. Small numbers of Gray Drakes are still hatching in the lower watershed. Brown Drakes have been reported in the Osborne Bridge area. Unfortunately, hot sunny weather has not produced the best conditions for mayfly dun emergence recently, while strong winds have not produced the best conditions for spinner falls either. Pro tip for avid readers who have stuck with the report this far: clouds, cooler temperatures and maybe a few showers are in the forecast for tomorrow, with slightly lighter winds than we have seen recently. That should produce near-optimal conditions for emergence of mayfly duns of several different species tomorrow on all river reaches. 

The upper river is hosting its usual month of June fly fishing crowds, so your “on the water diplomacy” will be tested whether you wade or fish from a boat.   Water quality is good with near or a bit below normal flows but these can vary throughout the irrigation season.

Henry’s Fork, June 14th 2024

Green drakes are controlling top water fishing up and down the river. They are coming out best on the lower river for now. The big stoneflies have peaked in numbers, but enough remain that trout will take floating imitations of them. Here is the basis for a strategy. The nutrient mass of a single drifting giant stone fly equals that of about 4 or 5 drifting green drakes or about half of this range for golden stoneflies. So rising once to grab one big stone fly means less expended energy that the rises to grab 4 or five
green drakes. Get the drift (no pun intended!)?
Currently good water quality reigns in temperature and clarity throughout the upper river and on downstream at least to Chester Dam. From this location, Fall River brings in run-off water in amounts that compromise this status.

Henry’s Fork, June 12th, 2024

Green Drake Madness is Here

Golden stoneflies are around with best numbers on the upper river. Caddis are everywhere. Now the major mayfly hatches are taking over on the lower river and moving on up in a major sense. Green drakes, PMDs with PM BWOs will make up the major activities for weeks to come. Fishing the river on the Flat Ranch Preserve is OK, but because so little water was released from Henry’s Lake earlier in the spring ( about 45 cfs maximum ) fish flushed in from the lake are down in number compared to years when 100 cfs and more were released.

Water Quality Information from Dr. Rob Van Kirk’s SWE Report Filed Yesterday

Water quality is excellent throughout the watershed. Turbidity is below average watershed-wide, and dissolved oxygen concentrations are good to excellent. Water temperature was above average again yesterday although within the optimal range for trout growth and activity at most locations for most of the day. Hatch timing is within a day of average watershed-wide.

Rob Van Kirk, Ph.D.

Science and Technology Director

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, June 8th, 2024

Golden Stone

Giant stone flies are on the wane on the lower river, but golden stone flies are coming on. With the current warm weather giant stone flies are flying through the upper river. With that going on and because of our almost ever present wind, dry stonefly patterns will be effective through the upper river. Remember: trout are in the water 24/7 and with wind spreading the bugs to all the river, fish will respond to correctly drifted patterns even in such as the Last Chance and Harriman locations because of canyons above and below. Soon big stonefly and golden stonefly activity will be gone, caddis activity will stay strong, then the mayfly season will begin with unequaled activity of various species from drakes to smaller versions, all that makes the Henry’s Fork so famed.

Currently good water quality reigns in temperature and clarity throughout the upper river and on downstream at least to Chester Dam. From this location, Fall River brings in run-off water in amounts that compromise this status.

Henry’s Fork, June 5th, 2024

The lower river is the best place to catch the giant stone fly hatch. Good numbers have yet to fly along the upper river, but upcoming warm weather will bring them out big time there. Also such weather will bring out recreational boaters, so some ” Share the River ” actions will be necessary in many locations. Consider that other major aquatic insects will begin appearing in good amounts soon to supplement those (large stoneflies, BWO, midges, caddis) being active with the warming weather.

Water Quality Information from Dr. Rob Van Kirk’s SWE Report Filed Yesterday

Water quality is excellent throughout the watershed. Turbidity is lower than average for this time of year throughout the watershed, and dissolved oxygen is above average. Water temperatures were cooler than average yesterday and even a little below the optimal range for trout growth and activity in most reaches. Hatch timing is within one day of average at most locations but is likely to move up a little over the next two weeks as much warmer weather is in store.

Rob Van Kirk, Ph.D.

Science and Technology Director

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, June 1st, 2024

The lower river above Chester Dam remains offering the most consistent fly fishing in the region. Caddis populations are expanding and PM BWO activity brings fish up reliably. Streamer patterns work during low light conditions. But the big story is the giant stonefly activity of which trout are now aware. The lower river now features the peak of activity, and the best way to approach fish keying on these big bugs is to begin above the hatch and work down into it. For now that means from the Riverside Campground area downstream to the Chester Dam to Ashton Dam. With warming weather hatch intensity moves upstream into such as Box Canyon and Coffee Pot. Size is the most important aspect in pattern selection. Presentation is easy: place it just a few feet above a rising fish several seconds after its last rise,or make a long drift over an area were a number of fish are rising.

Water Quality Information from Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed May 31st, 2024

Water quality remains good to excellent throughout the watershed. Turbidity is lower than average for this time of year throughout the watershed, and dissolved oxygen is above average. Water temperatures have cooled a bit over the past few days but will increase over the next few days. Hatch timing is within one day of average at all locations—generally a little behind average. However, I expect it to catch up to average if not get a hair earlier than average over the next week due to warmer temperatures. A very short period of high runoff would provide a greater chance of fill than a long period of relatively low runoff. Right now, weather forecasts favor the former scenario. Regardless, current reservoir volume is already higher than its peak volume last year, which is higher than it had been in several years.

Rob Van Kirk, Ph.D.

Science and Technology Director

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CEL

Henry’s Fork, May 24th, 2024

Looks like the big stoneflies will be laying low until Memorial Day itself. In fact, a lot of insects ( excepting midges and BWOs) will be doing the same because of snow showers coming and going likely for the next few days. When weather warms up, as predicted for Monday, there will be a lot of fly fishers wading and boating on the river from lower Cardiac Canyon downstream to Chester. So here are a few locations to try where a minimum of fishing company will be present.

Bear Gulch requires walking from the old ski area parking lot, no quite a mile, to the river. Some of the thickest and earliest giant and golden stone fly hatches on the entire river happen here, and hard sided boats of any kind are very rare because the slide access below Lower Mesa Falls is prohibited to such. Expect to see some rafts passing through. Allow a few days of warm weather and other great boat- free and minimum wader locations will see the big stoneflies become active. First is above the river in Mesa Falls State Park. Walk upstream above the Park, and fish some great boat-free water. Another is the river above the signed West Hatchery Ford road going off Highway 20.. This side of the river is almost free of boats and not many wading anglers. The reason is that the boat take-out location is on the more popular east side of the river and closed to boating beginning right below. Walk upstream on an old game trail for a while to get above the cliffs and fish as long as time permits. Another walk-in only location is around Sheep Falls. The road to this area is sign and just downstream from the West Hatchery Ford Road.

As the hatch moves upstream, we will keep track of its progress. With warming weather and sufficient time, such as Box Canyon and Coffee Pot will feature their share of active big stone flies. By then choosing a great location almost anywhere on the Henry’s Fork will become more complicated as other great insect hatches will begin!

Some Details From Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed Yesterday, May 22nd.

Mean temperature yesterday was 8 degrees F below average, and precipitation was recorded at only one station. That kept snowmelt rates low and water-year total precipitation at 99% of average. Net change in snow water equivalent (SWE) was 0.2 inches of melt, compared with 0.5 inches on average. Remaining SWE is 53% of this year’s peak, compared with 57% on average, and current SWE is in the 45th percentile for the date.

Weather forecasts call for continued below-average temperatures through Sunday, with precipitation possible every day. Mid-elevation snow will continue to melt as it did yesterday at slightly below-average rates. High elevations will likely gain new snow today and tomorrow. Long-term outlooks call for very warm and dry conditions starting early next week and continuing for the foreseeable future. That will accelerate snowmelt at all elevations.

Water Quality

Water quality improved again yesterday, as turbidity continued to drop at all locations except immediately downstream of Island Park Dam. Dissolved oxygen concentrations are above average in all river reaches, and water temperatures were within the optimal range for rainbow trout egg and fry development watershed-wide. Hatch timing is within 1–2 days of average at all locations and will slow by a day or so over the next few days.

Rob Van Kirk, Ph.D.

Science and Technology Director

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CEL

Henry’s Fork, May 18th, 2024

Big Time Trout Food

The stone fly hatch on the lower river is beginning right on time. From Ashton Dam down to the Chester Dam nymphs are crawling onto banks. It will take some warm weather to advance the hatch in numbers, molting to adults, and to fly over the river. So until warm weather arrives, big nymph patterns simulating these insects will be among the most effective to use as resident trout key on such patterns. During this week the hatch should advance, and we will provide information on best locations to enjoy it into Memorial Day weekend.

By any measure the big stone fly appearance ends the so called shoulder season on the river. From now on high interest applies to the season long advance of insect life which makes fishing the river so famous. We at Fly Fish Food-Jimmy’s will monitor this advance on the river and provide solid information on it throughout the season.

Water Quality Statement from Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed Yesterday, May 17th.

Water quality continues to be good throughout the watershed. Water temperatures and dissolved oxygen concentrations are good to excellent and near average for this time of year. Turbidity continues to drop in the Warm River to Ashton reach and is also starting to drop downstream of Fall River. I do not expect abnormally high turbidity anywhere in the watershed for at least a week. Hatch timing is within a day of average at all locations and is likely to stay very near average for the next few days. Cooler weather next week could slow things down a bit then, but I expect average timing for the salmonfly hatch watershed-wide. Salmon fly adults have just started emerging in the spring-fed locations such as Buffalo River and Warm River, indicating just a few more days before they begin to hatch in large numbers in the reach between Ashton Dam and Chester Dam.