Henry’s Fork

Henry’s Fork, October 8th, 2022

Next week during October 11th & 12th, IDF&G will be doing an electroshocking survey from Warm River to Ashton. The purpose is to study the Rocky Mountain whitefish health status and population. Until some unsettled weather moves in no change in fishing strategy should take place. Look for BWO, mahogany, and caddis activities peaking during PMs and during day time warmth hopper and ant patterns being effective. Streamers presented around first light, during evenings, and any low light conditions will be increasingly effective for migrating brown trout throughout the lower river.

Henry’s Fork, October 4th, 2022

Brown trout are migrating to spawning areas throughout the river below lower Mesa Falls. In contrast to the brown trout runs in Yellowstone park waters, the Henry’s Fork run is attended primarily by local fly fishers. Thus with fewer anglers on the river, a better chance of solitude can be realized.

In addition, the lower river still offers good terrestrial insect hatches on sunny, warm days and BWO, mahogany dun, and caddis activity. So the river offers good fishing for the top water enthusiast as well as those preferring to try wet flies to encounter the migrating brown trout.

Henry’s Fork, September 27th, 2022

Look for fishing to improve, especially because of BWO and mahogany dun activity later this week, as unsettled weather is in the forecast. Streamer fishing will be picking up almost everywhere along the river. Box Canyon, the lower river and the Tubs in particular, should be some of the best locations for trying streamers. Mid afternoons should offer the best fishing in response to terrestrial insect activity.

Headlines:  from Dr. Rob Van Kirk’s Henry’s Fork drainage water status report from yesterday follow.

• Mean temperature was above average yet again yesterday; water-year precipitation is 92% of average and may end the water year there, given a good chance of showers later this week.
• Natural flow has dropped over the past day or two, while diversion has increased a little.
• Island Park Reservoir dropped by 35 ac-ft yesterday and is 45% full, compared with 46% on average. Current outflow is around 400 cfs and should stay there for the rest of the week.
• Water quality: Turbidity at Island Park Dam has been fluctuating 1-2 turbidity units on either side of average; turbidity is at or below average at all other locations.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, September 24th, 2022

The Box Canyon remains a good choice with streamer and rubber leg patterns being effective. Submerged weeds are breaking here and on downstream through the Harrriman Park reach. On warmer days, until a killing frost arrives, hopper, patterns with and without a dropper as well as those for beetles and ants are effective anywhere on the river. The best happening on the lower river is the cooling weather. Because of it, trout are responding there to BWO and mahogany dun activity in a better measure, with streamer patterns being effective during low light conditions.

Henry’s Fork, September 20th, 2022

The Henry’s Fork features many famed locations. These tend to overshadow lesser known sections. The Tubs area is a location that takes a back seat to famed locations because its best fishing is seasonal and begins now. Most recreational boating from Big Springs to Mack’s Inn has ended, and trout migrating downstream from the Flat Ranch area reside in the deep holes here. As autumn advances these trout, as well as residents, become increasingly interested in streamer patterns. So sink-tip lines and stout leaders are in order. Very large whitefish ( stiffies) are present and are always feeding on midges. If you own a smoker and are looking to stock it, The Tubs offers stiffies ranging up to near three pounds. For sure, midge life cycle patterns will interest them.

Headlines from Dr. Rob Van Kirk’s Henry’s Fork drainage water status report compiled yesterday follow:  

• Well above average temperatures returned yesterday; mean temperature for September so far is 5 degrees above average.
• Natural flow stayed relatively constant yesterday and is 74% of average.
• Island Park Reservoir is 45% full, compared with 46% full on average. Outflow will be decreased again today to around 350-400 cfs.
• Water quality: Turbidity at Island Park Dam decreased yesterday and is back below 5 turbidity units this morning, about average for this time of year.

Henry’s Fork, September 10th, 2022

Cooling and upcoming unsettled weather is just what is needed to bring back daytime action on the lower river. BWO and mahogany dun activity will be on the increase, and barring a killing frost, hoppers and other terrestrial insects will continue to attract trout and steamer patterns will be effective during low light conditions. Until killing frosts take place presenting terrestrial insect patterns is a best straregy for fishing the entire river

On the upper river, Box Canyon will begin producing some great streamer fishing to go along with good results from presenting large nymph patterns, and the same can be expected in the Tubs area below Big Springs.

About a week ago flow out of Henry’s Lake was reduced to around 35 cfs from around 150 cfs. That action will move larger fish out of the Flat Ranch reach of the river and into the river above Mack’s Inn. Look for many of those fish to reside in the Tubs area of the river.

Henry’s Fork, September 6th, 2022

Visits to the upper river are decreasing significantly, and presenting terrestrial insect patterns is the best way to find daytime fishing success. Speckled dun and caddis activity provide lesser daytime action while tricos bring on early in the day action before increasing air temps awaken terrestrial insects. With shorter daylight hours and colder nights, water in the lower river will begin to cool to the point that fall may lfy activity will begin.

Headlines from Dr. Rob Van Kirk’s Henry’s Fork drainage status report of yesterday follow. :  

• High temperature records were broken on five of the last six days, and dry weather has dropped water-year total precipitation to 90% of average.
• Natural streamflow and diversion have dropped very slowly over the past few days.
• Outflow from Henrys Lake was decreased on Saturday, so Island Park Reservoir is now dropping at around 1000 ac-ft/day at 970 cfs outflow.
• Water quality: Because of warm water temperatures in Island Park Reservoir, dissolved oxygen concentration dropped over the weekend, necessitating transfer of some outflow from the power plant back to the gates. That caused a slight increase in turbidity, but it remains near or below average at all locations in the watershed. Despite hot air temperatures, shorter day length and lower sun angle have kept water temperatures out of the stressful range at all locations, as expected. Afternoon high water temperatures have dropped steadily at all locations for the past four days and stayed below 70 degrees at all locations yesterday. Water temperature at Pinehaven has stayed below 68 degrees for the past four days. Expect water temperatures to continue to drop incrementally over the next two days and then more substantially as cooler weather arrives later in the week.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

[email protected]

Henry’s Fork, August 30th, 2022

Be ready with terrestrial insect patterns anywhere on the river. Honey, also called cinnamon, ants are showing up along the upper river, and the trout love them.

Below are Dr. Rob Van Kirk’s status report headlines for the Henry’s Fork drainage.as of yesterday.

Headlines:  

• Yesterday’s low temperature was the coolest since June 30, but the daily mean was average for the date.
• At 72% of average, natural flow over the past week is 2^nd lowest on record, just ahead of 2016. No drought relief is in sight, as very hot, dry weather is expected for the next two weeks.
• Island Park Reservoir is dropping at around 800 ac-ft/day and is 54% full, compared with 50% full on average.
• Water quality: : Afternoon high water temperatures were a little higher yesterday than on Sunday at most locations due to warmer weather. However, water temperatures stayed below 68 degrees at all locations. I expect afternoon high water temperatures to climb back up to 70 degrees or higher over the next few days at Pinehaven and St. Anthony. Water temperatures at all other locations will likely stay below 70 degrees due to shorter days and lower sun angle. In particular, the reach between Warm River and Ashton is shaded much of the day now and will not absorb nearly as much solar radiation as the reaches upstream of Pinehaven and St. Anthony.Water quality was good yesterday across the watershed, but afternoon water temperatures are likely to reach 70 degrees again at the warmest locations.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

Henry’s Fork, August 20th, 2022

The number of recreational floaters is increasing on every section of the river. Weekends bring these folks out “en masse” at certain locations They can cause particular problems at boat launch sites because they have yet to develop an etiquette protocol, so be understanding at these locations and on the stream. When reasonable recreationists are encountered, try explaining to them the bases for developed launching and debarking manners as well as for keeping polite distances away from active anglers. These folks, too, have a right to enjoy the river, but they also have an obligation to others to do so in a considerate manner.

Henry’s Fork, August 16th, 2022

Terrestrial insect patterns are the best bet for action almost everywhere on the river during daytime hours.

Headlines from Dr. Rob Van Kirk’s water report submitted yesterday for the Henry’s Fork drainage follow.

Headlines:  

• After a dry day, water-year precipitation stayed at 91% of average, ranking 12^th driest out of the last 33 years.
• Natural flow is receding from the effects of Saturday’s rain, but proportional decreases in diversion are keeping lower-watershed streamflow ahead of target flows.
• Updated data show about a 5% improvement in natural flow upstream of Island Park Reservoir since this time last year.
• Water quality: Peak water temperatures were about where they were on Sund

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

208-652-3568 FAX

• ay, but morning lows yesterday were the coolest in 5-6 days at all locations. Turbidity is at or below average at all stations upstream of Warm River and well above average at all stations downstream.