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Henry’s Fork

Jimmy's All Seasons Angler / Henry’s Fork (Page 5)

Henry’s Fork, August 2nd, 2023

Flow out of Island Park Dam has been reduced to the usual amount for this time of the season. Up and down the river AM spinner falls and terrestrial insects are abundant. Hopper and ant patterns and hopper-dropper rigs work anywhere during PMs. Long, drag free floats are are required with any of these. The above photo should be enough to tell you that in many locations, terrestrial insect populations are not only abundant but the major food form for trout this time of year. If you are experienced in long, drag free floats, consider using a slightly stronger tippet in order to play that trout quickly giving it a better chance to survive the warmer summertime waters..

One other thought; particularly in the Big Springs- Macks Inn, Box Canyon, Harriman State Park and Warm River to Ashton sections, recreational boaters abound. This means early AM spinner fall periods and late afternoon terrestrial insect activities are best conditions for minimizing interruptions.

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Henry’s Fork, July 22nd, 2023

The Tubs

Water Quality Information from Dr. Rob Van Kirk’s Henry’s Fork Drainage Report Filed Yesterday.

Water quality continues to exceed expectations throughout the watershed, especially given hot dry weather and very high reservoir outflow. Water temperatures yesterday were a little cooler than on Wednesday due to cloud cover and close to average. Afternoon high water temperatures exceeded 70 degrees at our usual warm spots—Buffalo River, Pinehaven, St. Anthony, and Parker—but the duration and magnitude of temperatures greater than 70 degrees was lower than on Wednesday. Water temperatures stayed within the optimal range of 53–68 degrees all day at all of our other sonde locations. Dissolved oxygen continues to stay good to excellent—and above the state cold-water standard of 6 mg/L—at all locations.

Turbidity is still well below average at all locations between Island Park Dam and St. Anthony and among the lowest readings we have observed during mid-July since first installing our water-quality network in 2014. This is despite outflow through Island Park Dam gates higher than we have seen this time of year since 2013. The common denominators among the years with lowest turbidity—2017, 2018, 2019, and 2023—are near- to above-average snowpack and high Island Park Reservoir levels.

Timing of aquatic insect hatches is still around 5 days later than average in the river reach between Island Park Dam and Pinehaven, 8 days later in the Warm River to Ashton reach, and 4 days later than average between Ashton Dam and St. Anthony.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

There are a few comments on why we continue to place Dr. Rob’s observations on the fishing report. We do so because many of these give reasons for fly fishing success. They also help in deciding where and when to try your luck on drainage waters.

Consider that although aquatic insect hatches remain a bit late in much of the drainage, terrestrial insect populations are building and are becoming quite important as a trout food along the entire river and its tributaries.

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Henry’s Fork, July 18th, 2023

With the warming weather and bright skies up and down the river, it is time for terrestrial insects to become an important food form for trout.. That means long, drag free drifts in front of well vegetated banks and dry structure such as snags, rocks and logs. Have hopper, ant, beetle, and even crane fly patterns on hand.

A productive trick follows: I swat any horsefly that lands on my self, then toss the splatted results into the water to drift downstream. On hearing or seeing a trout rise to take it, I have located another fish to try. Do the same with hoppers or any other resident terrestrial insect to locate a feeding fish. You might be accused by your fishing partners of low grade chumming, but the act is legal and informative!

Henry’s Fork at Bear Gulch

Water quality information from Dr. Rob Van Kirk’s Henry’s Fork drainage water status report filed yesterday.

The big (positive) story continues to be how well water quality is holding up so far this summer, despite high outflow from Island Park Reservoir and warm weather. Water temperatures have stayed near average and well below last year’s readings at most locations. Daily maximum water temperatures exceeded 70 degrees yesterday at Buffalo River, Pinehaven, at St. Anthony and Parker. However, both duration and magnitude of high water temperatures are lower than at this time last year. For example, water temperature exceeded 70 degrees at Pinehaven yesterday for a little under 6 hours yesterday, compared with 7.5 hours on July 16 2022. Maximum water temperature yesterday was 71.8 degrees F at our sonde, compared with 72.9 degrees last July 16.

Turbidity is well below average at all locations except Flat Rock, where relatively high outflow from Henry’s Lake has kept turbidity a fraction of a turbidity unit above average.

Timing of aquatic insect hatches is still 5–6 days later than average in the river reach between Island Park Dam and Pinehaven, 8 days later in the Warm River to Ashton reach, and 4 days later than average between Ashton Dam and St. Anthony. At this point, I do not expect much change with respect to average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

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Henry’s Fork, July 15th, 2023

Flav

The river below Ashton Dam is beginning to warm to the point that best fishing is early or late in the day. Big stonefly activity and the same for drake mayflies is about over. Afternoon caddis action remains , and PMD and flav spinner falls at these times of day will bring some top water action. Streamers can also be effective when direct sun light is off the water. Big bows and browns come out to forage at these times because of increased overhead cover.

After the July 10th increase in flow out of Island Park Dam, conditions have stabilized in the river below. Brown drake, flav, little PMD, and afternoon caddis activity still provide top water fishing with AM spinner falls and evening action. Expect recreational floaters to increase during day time hours.

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Henry’s Fork, July 11th, 2023

Water quality and insect hatch Information from Dr. Rob Van Kirk’s Monday drainage water status report

Water quality us holding up well and is better than average for this time of year. Mean daily water temperatures have stayed at or below average and below last year’s values at all stations except Parker. Daily high water temperatures have exceeded 70 degrees over the past few days at Buffalo River, Pinehaven, St. Anthony, and Parker. Peak water temperatures are happening between 3:30 p.m. and 8:30 p.m. now. Dissolved oxygen concentrations are good at all locations.

Turbidity at Pinehaven increased briefly to 4.0 NTU on Friday as expected but has since dropped to less than 3.0 NTU, where it was prior to Friday’s outflow increase. For comparison, average turbidity values for the date are 6.1 NTU at the dam gates and 4.5 NTU at Pinehaven, Last year’s daily values on July 10 were 9.4 NTU and 7.9 NTU, respectively.

Timing of aquatic insect hatches has not changed much with respect to the 2014–2022 average over the past two weeks, as water temperatures have stayed close to or slightly below average. Hatch timing in the river reach between Island Park Dam and Pinehaven is 5–6 days later than average but at or a few days ahead of that in 2022.

Flow out of Island Park Dam was raised to about 1300 cfs yesterday, and since July 4th its progress graph looks like a step function as irrigation water demands kick in.The most significant insect happening is the building evening brown drake activity on the river below the US Highway 20 Bridge aside from AM spinner falls throughout the upper river. Especially from in Box Canyon down to Last Chance you will see the peak of recreational activity. Be patient and show the floating public that fly fishers are a “polite bunch.” ‘. The best way to escape the bulk of the plastic/rubber flotilla is during AM spinner falls and evening brown drake activity.

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Henry’s Fork, July 7th, 2023

Big Osborn Spring at Lower Right

Fishing in the upper section of the Harriman State Park section will soon take a somewhat back seat during PMs to the lower section. March browns are mostly gone, Green Drake activity is tumbling, PMDs are getting smaller in size, but flavs remain for good PM fishing and AM spinner falls. But for brown drakes, the peak hatch peak is soon to come, and the best of their hatch will be accessed via Wood Road 16 (WR 16). For sure there will be some brown drakes throughout the entire Harriman reach (same with flavs), but there is one big reason why the best concentration is on the lower section. See the above photo? It was taken of a river section about a half mile above the WR 16 access.The US Highway bridge is at upper right. What is significant here is that water flowing from Last Chance on down to and past the bridge is warming because of water in Island Park Reservoir and inlets from Silver and other Park lakes are warming (all are shallow), and so is weather, helping to diminish dissolved oxygen in the river. However inflow from Big Osborn Spring adds a large amount of cool water to the river making better conditions for the brown drake population in the river below. Brown drakes emerge best during evenings but they are sure to peak soon. Fish are in the river “Twenty-Four Seven” and they will be gorged on these active insects just before their emergence peak. So consider being on this part of the river very soon. .

Water Quality Section from Dr. Rob Van Kirk’s Henry’s Fork Drainage report filed July 3rd.

Overall, water quality continues to be excellent throughout the watershed, with the exception that afternoon high temperatures are starting to exceed optimal at some locations. Mean water temperatures yesterday were very close to average throughout the watershed, but afternoon highs exceeded 70 degrees at Buffalo River, Pinehaven, St. Anthony, and Parker. Dissolved oxygen concentrations are good in all river reaches.

Timing of aquatic insect hatches has not changed much with respect to the 2014–2022 average over the past week except at Marysville, where it has moved from 9 days later than average to 8 days later. Hatch timing in the river reach between Island Park Dam and Pinehaven is 5–6 days later than average but at or a few days ahead of that in 2022. Hatch timing at Flat Rock, Ashton Dam, and St. Anthony is still 1–4 days behind average but 1–3 days ahead of last year.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

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Henry’s Fork, June 30th, 2023

Golden stone flies are still around up and down the river. Some may flies have peaked (green drakes, gray drakes, March browns) and others are yet to peak ( brown drakes and flavs on the upper river). Afternoons will be the best times for finding the brown drakes and flavs.

The other happening that will begin its season is recreational floating. Going through Box Canyon and Big Springs to Mack’s Inn will have the biggest concentrations, but they will also be common through Harriman State Park to Riverside campground. Be patient with these folks as most of them have yet to form an etiquette. Gently explain to them that you realize they have a right to the river, but we appreciate you giving anglers present enough room to enjoy what they do. To be sure, you will learn a lot about human nature through these encounters.

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Henry’s Fork, June 27th, 2023

Upper Coffee Pot Area

Water Quality and Insect Hatch Information From Dr. Rob Van Kirk’s Henry’s Fork Watershed Report of Today

Overall, water quality continues to be excellent throughout the watershed. Turbidity continues to decrease across the watershed. Water temperatures yesterday were near to slightly below average throughout the watershed. Temperatures were within the optimal range for rainbow trout most of the day in most river reaches. Dissolved oxygen concentrations are optimal.

Timing of aquatic insect hatches at Flat Rock, Ashton Dam and St. Anthony is 1–4 days later than the 2014–2022 average but 1–4 days earlier than last year. Hatch timing in the river reach between Island Park Dam and Pinehaven is 5–6 days later than average but at or a few days ahead of that in 2022. Hatch timing lags average by the largest margin at Marysville, where it is 9 days later than average.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Dr. Rob Van Kirk’s information above explains why fishing is better on some parts of the river than others. For example a good population of big stoneflies remain in Box Canyon, but on cool, cloudy days streamer fishing produces best. Golden stoneflies are coming out up and down the river., Gray drakes and flavs are showing up during PMs on the river below Ashton Dam. The fabled green drake hatch is yet to be significant in the Harriman State Park reach and is declining on the lower river.

The lower Coffee Pot area will one of the better locations to find relative solitude on the river. The Henry’s Fork giant stonefly hatch ends there, and golden stone fly, PMD and caddis activities can bring on good fishing.

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Henry’s Fork, June 24th, 2023

Green Drakes are out on the lower river with best concentrations below Ashton Dam to above Chester backwaters. Although they inhabit many section of the river, this is the best hatch in terms of numbers. They may have peaked here, but there are enough to make a visit worthwhile. Days with higher relative humidity, little wind, and even overcast will bring out the best concentrations. But as with the feeding on stoneflies a few weeks earlier, they will become filled and head to the depths to digest. A strategy is to give them time to digest, then come back later with life form patterns, and you will have some action.

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Henry’s Fork, June 20th, 2023

The Tubs

Here is some good info from Dr. Rob Van Kirk’s Water Status report filed yesterday for the Henry’s Fork watershed.

Water quality

Overall, water quality continues to be excellent throughout the watershed. Turbidity has increased a little at most locations over the past day or two due to rain but remains much lower than it had been during the peak of snow melt a few weeks ago. Water temperatures are in or slightly below the optimal range for rainbow trout watershed-wide. Dissolved oxygen concentrations are also optimal. Timing of aquatic insect hatches at Flat Rock, Pinehaven, Ashton and St. Anthony is staying around 1–4 days later than average but 1–3 days earlier than last year. Hatch timing at Marysville and Island Park Dam is 7–8 days later than average and about 1–3 days later than last year. I do not expect hatch timing to change much with respect to average for the foreseeable future.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Consider that Dr. Rob is talking about the peak of insect hatches. This means that a few insect are emerging now, but achieving peak concentrations are delayed.

The above photo shows The Tubs area above Mack’s Inn. Try pitching streamer patterns into these deep holes. You will find some relative solitude before recreational floating gets going.

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