Henry’s Fork

Henry’s Fork, April 20th, 2024

All boat launch facilities below Ashton Dam are open. The Stone Bridge-Warm River site above is snowy.

The lower river offers the most consistent and best stream fishing in the area. Midge, BWO, and diminishing March brown hatches are bringing fish up resulting in good top water fishing during low wind days with afternoons being best. Traditional nymph and rubber legs patterns presented at the heads of deep water and through runs are effective and streamer patterns presented under low light conditions attract brown and large post-spawning rainbow trout.

No significant run-off from Fall River to date. Water contributed from Fall River above all irrigation diversions is clear, cold and currently about normal.

Info from Dr. Rob Van Kirk’s Henry’s Fork Drainage SWE Report filed yesterday, April 19th, 2024

Generally dry conditions are expected for the next 5–6 days, with temperatures near average. I expect snow melt to resume this weekend, although it will not be as rapid as what we saw last weekend. All forecasts are indicating a wet period starting in the middle of next week and continuing through the rest of the month. Temperatures during that time will be near to slightly above average. Natural stream flow decreased by 10% yesterday as the effects of much colder temperatures in headwater areas made their way down to the middle of the watershed, where I calculate natural flow. Yesterday’s watershed-total natural flow was 109% of average for the date: 93% in upper Henry’s, 102% in Fall River and 156% in Teton River.

Henry’s Fork, April 12th, 2024

The information below reveals that run-off has begun only in the Teton River drainage and is reflected by around or slightly more than normal flows in the lower river down to the Teton River confluence. It also suggests that the next few days will offer the most comfortable times to enjoy trout responding to BWO, March brown, and midge activity.

Rob Van Kirk, Ph.D.

Details From Dr. Rob Van Kirk’s SWE Report Filed Yesterday, April 11th, 2024

Snow melt increased natural flow in the Teton River yesterday (120%) while flow in the Fall River 76% 0f normal and 78% of normal in the Henry’s fork..These amounts will increase until Monday when cooler atmospheric temperatures will begin to take place for several days.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, April 6th, 2004

Cloudy skies are great for increasing the density of BWO, March Brown, and midge activity. But the stronger the wind the bigger the negative impact on these activities. That wind is happening now on the lower river, making evenings and early AMs the best times to enjoy fish responding to these activities. Improved weather is predicted for later next week, but be aware we are entering the run-off season as warm weather begins to dominate. If you are fishing streamers, the only impact wind has is on casting precision!

Headlines 4/5 From Dr. Rob Van Kirk’s SWE Report Filed April 5th for the Henry’s Fork Drainage

• The last four days were warm and dry, dropping water-year precipitation to 103% of average and melting over 0.5 inch of SWE from Sunday’s peak.
• Natural stream flow has increased by 15% since Sunday due to snow melt and is 95% of average.
• After a few days of showers and cooler temperatures, very warm, dry weather is expected next week.
• The upper Snake River reservoir system is 90% full, compared with 71% full on average.

Details

Dry conditions are expected for 7–10 days starting early next week. That will initiate widespread melt of snow at all but the very highest elevations.

Natural stream flow has increased by over 15% since Sunday due to snow melt. Natural flow was 95% of average yesterday: 90% in upper Henry’s Fork, 97% in Fall River, and 104% in Teton River. I expect natural flow to continue to increase through tonight before cooler temperatures slow melt and drop stream flow over the weekend.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, March 30th, 2024

Major run-off has yet to reach the river as flows throughout are about normal for this time of the year. Based on Dr. Van Kirk’s information below, a greater than normal run-off could result from the high accumulation of snow in drainage streams originating in the Teton and Big Hole ranges and the southwest corner of Yellowstone Park. Look for run-off to begin as we warm in April and trout will hunker closer the bottom to pick off the abundance of drifting food forms. Right now on the lower river, BWOs and March brown mayflies and midges provide good top water fishing with best success during overcast days with little ( Is that possible?) wind. Presenting streamer, woolly bugger, and rubber leg patterns is also effective especially under these atmospheric conditions. Smaller nymph patterns drifted into holding water will also bring responses from resident salmonids. All this will change with the arrival of serious run-off. We will keep track of its progress to help with planning your fishing strategy.

Headlines from Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed March 29th

• Heavy precipitation yesterday increased the water-year total and SWE each two percentage points to 104% and 95% of average, respectively.
• Generally wet, cool weather is expected to continue for the foreseeable future.
• At an outflow of 449 cfs, Island Park Reservoir gained 354 ac-ft yesterday from precipitation and is 92% full, compared with 83% full on average.
• The upper Snake River reservoir system is 90% full and continuing to fill, despite 3500 cfs of diversion for managed aquifer recharge and 2500 cfs spill at Milner Dam.

Details

Mean temperature yesterday was right at average, and precipitation averaged 0.58 inch across the watershed, the highest one-day total since March 2. Precipitation heavily favored the upper Henry’s Fork sub-watershed and Yellowstone Plateau, where all five SnoTel stations in that area received at least 0.8 inch of water equivalent. White Elephant led all stations yesterday at 1.6 inches. Totals elsewhere in the watershed ranged from a few one-hundredths of an inch to 0.5 inch. This was enough to move the water-year total up two percentage points to 104% of average, ranking 12th out of the last 36 years (57th percentile).

New snow water equivalent (SWE) accumulations ranged from 0.2 inch at Grand Targhee and Pine Creek Pass to 1.7 inches at White Elephant. All stations in the Island Park/Yellowstone Plateau area received 0.9 inch or better. The day’s totals moved watershed-mean SWE up two percentage points to 95% of average, ranking 21st out of the last 36 years (43rd percentile). Current SWE is at its seasonal maximum at all nine stations. This ensures that annual peak SWE at Island Park will occur later than its statistical average, which is March 27. Average date of peak SWE at Pine Creek pass is March 30, and given current conditions and weather forecasts, this year’s peak SWE there will likely also occur later than average.

Henry’s Fork, March 16th, 2024

Limited access prevails along the lower river. BWOs are out and with an extra hour of daylight more time is available to enjoy trout responding to them. Expect the river to cloud a bit as the warm weather will enhance bank side and nearby melting.

Fun Farm Bridge

• Water-year total precipitation stayed at 106% of average, while SWE dropped a percentage point to 95% of average.
• Dry and warm weather is expected for the next six days.
• At an outflow of 416 cfs, Island Park Reservoir dropped by 92 ac-ft yesterday and is 91% full, compared with 80% full on average.
• The upper Snake River reservoir system is 88% full, compared with 68% full on average.
• Total reservoir storage plus existing snowpack across the basin is high enough that water will be spilled out of the system at Milner Dam starting on March 25.

Details

New snow water equivalent (SWE) over the past four days ranged from 0.2 inch at Pine Creek Pass to 1.7 inch at White Elephant. Current SWE is 95 of average: 92% in upper Henry’s Fork, 97% in Fall River, and 99% in Teton River. Current SWE ranks 17th out of the 36 years (54th percentile), just ahead of 1998 and just behind 2002. After the upcoming six days of dry weather in the forecast, SWE will fall to around 91% of average and drop several places in the rankings.

Dry conditions with above-average temperatures are expected for the next six days, before precipitation returns late next week. Valley snowmelt is expected, and that will increase streamflow a little. However, below-freezing nights will keep mid- and high-elevation snowpack intact before more mountain snow and valley rain is expected late next week. Long-term outlooks are leaning toward above-average precipitation, with gradually cooling temperatures 1–2 weeks out.

 

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

Henry’s Fork, March 9th, 2024

Rainbow spawning has begun at least on the lower river with most activity occurring under low light conditions. Thus it is vital not to disturb even unoccupied redds.because of the presence of fertilized eggs.

Headlines from Dr. Rob Van Kirk’s Henry’s Fork Drainage SWE Status Report Filed Yesterday3/9

• More precipitation from the Monday–Wednesday event trickled into gages yesterday, keeping the water-year total at 106% of average. SWE dropped to 95% of average.
• Modest precipitation is expected again next Monday–Wednesday.
• At an outflow of 373 cfs, Island Park Reservoir gained 45 ac-ft yesterday and is 91% full, compared with 79% full on average.
• The upper Snake River reservoir system is filling rapidly at 86% full, compared with 76% full on average.
• Today’s precipitation-type take-home: Increasing spring and summer air temperatures have a doubly negative affect on water quality, directly via water temperatures and indirectly via lower water supply.

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Most of the SnoTel stations lost a little snow water equivalent (SWE) yesterday to sublimation, which is typical on cold days following a large snow event. That put net storm-total SWE increase at 1.4 inches, ranging from 0.2 inch at Crab Creek to 2.5 inches at Black Bear. Current SWE is 95% of average: 100% in the Teton headwaters, 97% in Fall River, and 89% in the upper Henry’s Fork. The watershed average currently ranks in the 54th percentile across the last 36 water years.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

 

 

 

Henry’s Fork, March 2nd, 2024

Yes, the current storms have limited access to much of the river and its drainage. But consider that this unusual amount of snowfall means better potential for great fly fishing next season.

Headlines  From Dr. Rob Van Kirk’s Henry’s Fork Drainage SWE Report Filed March 2nd

• Moderate and more widespread precipitation yesterday ended a very wet month of February, increasing water-year total precipitation to 96% of average and SWE to 82% of average.
• Heavy precipitation is expected to continue for the next week, with the March monthly outlook leaning toward above-average precipitation.
• Mean outflow from Island Park Reservoir over the critical December–February period for trout survival was 411 cfs, 116% of average.
• Island Park Reservoir gained 4,732 ac-ft over the Dec–Feb period and is 90% full, compared with 78% full on average. Outflow will be reduced to 375 cfs next week to fill the reservoir a little faster.
• The upper Snake River reservoir system is filling rapidly and is 83% full, compared with 66% full on average.

Details

As important as the warm temperatures may end up being later this spring for reservoir ice-off and subsequent water quality, the bigger story of February 2024 was precipitation. The watershed mean for the month was 5.18 inches, 142% of average. February precipitation totals were 127% of average in Fall River headwaters, 130% of average in Teton headwaters, 143% of average in upper Henry’s Fork, and a whopping 218% of average in the valleys. That moved water-year precipitation from 84% of average at the beginning of the month to 96% of average this morning, ranking 18th out of the last 36 years.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

 

 

 

Henry’s Fork, February 24th, 2024

This weekend looks like a good time to enjoy midge activity on the lower river before another stormy week begins on Monday. A bonus could be the first, but minor appearance of BWOs on the lower river. Consider that the rainbow trout spawning season is beginning. So lets allow them to do so in peace. It is in our best interests if we want his event to replenish their population for years coming up.

Headlines From Dr. Rob Van Kirk’s Snow-Water Equivalent (SWE) Report Filed 2/24 for the Henry’s Fork Drainage

Light precipitation yesterday kept the water year total at 96% of average and SWE at 81% of average.

• A major winter storm is still expected on Monday and Tuesday, with additional precipitation later next week.
• At an average outflow of 451 cfs, Island Park Reservoir dropped by 112 ac-ft yesterday and is 90% full, compared with 78% full on average.
• The upper Snake River reservoir system is filling rapidly and is 81% full, compared with 62% full on average.

Details

Natural flow stayed fairly constant yesterday at 96% of average: 91% in upper Henry’s Fork, 110% in Fall River, and 92% in Teton River. This is the largest difference between this year and 2016. Cumulative natural streamflow so far this water year over the Henry’s Fork watershed is 97% of average, ranking 25th out of the last 47 years (48th percentile–pretty close to the middle of the pack). On the other hand, natural flow at this point in water year 2016 was only 81% of average, ranking 42nd out of the 47 years.

So, while we know that warm late-winter and early spring temperatures cause poor water quality in Island Park Reservoir, we also know that natural streamflow into the reservoir counteracts that effect. Higher inflow produces better water quality. So, while climatic factors so far this winter look very much like 2016, the watershed is in much better shape this year than it was in 2016, thanks to above-average snow last year and to above-average precipitation in the late summer and early fall. The solid February we are having will also help. Lastly, water conservation measures implemented in 2018 by our agricultural partners, Fremont-Madison Irrigation District, and US Bureau of Reclamation have greatly reduced irrigation-season drawdown of Island Park Reservoir over the last six years, which will also help limit the negative effects of warm temperatures and low snowpack on Island Park Reservoir this summer.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL

Henry’s Fork, February 17th, 2024

Headlines from Rob Van Kirk’s Henry’s Fork Drainage Snow-Water Equivalent (SWE) Report Filed Yesterday

• Heavy precipitation yesterday moved the needle substantially, as water-year total precipitation increased to 97% of average and SWE to 81% of average.
• Lighter precipitation will continue off and on for the next week.
• Natural flow increased to 102% of average yesterday due to very warm temperatures.
• At an average outflow of 465 cfs, Island Park Reservoir gained 111 ac-ft yesterday and is 91% full, compared with 77% full on average.

Details

In recent years, we have seen the month of February turn a below-average snowpack into an above-average snowpack. The most striking example was 2019, when SWE improved from 79% of average on January 31 to 121% of average on February 28. Could that happen this year? Probably not with respect to snowpack, although February may bring water-year total precipitation back up to average. Total precipitation for the first 15 days of February has exceeded the monthly mean already, so February will definitely be the first month of above-average precipitation since October and will likely rank in the top 10 for February precipitation. If we receive average precipitation for the rest of the month—which is very likely—the water-year total will stay at 97% of average. However, current outlooks give a decent chance of above-average precipitation late in the month, so we could end the month a percentage point or two higher 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

  Why do we offer this information ?

Much of the SWE information Dr. Van Kirk collects then offers on the Henry’s Fork drainage impacts the water quantity and therefore angling quality of the upcoming season. And that quantity is determined mainly by the snow accumulation of the previous winter. The activity of the salmonid population and the availability of the aqueous forms on which they feed are impacted by the amount of water in which they live. The fly fisher benefits from this information with respect scheduling visits that will provide the best chance for a satisfying angling experience. The fly fishing retailer benefits through helping to decide when to offer items ( flies in particular) specific to the time of the season.

Henry’s Fork, February 10th, 2024

Midge hatches offer good top water fishing during pleasant mid days. Rainbow trout on the lower river are beginning their spawning mode. Please avoid disturbing any spawning fish as well as their redds.

Headlines from Dr. Rob Van Kirk’s Henry’s Fork Drainage SWE Status Report of Report Filed Yesterday

• Precipitation focused in the upper Henry’s Fork yesterday increased water-year total precipitation for the watershed to 94% of average and SWE to 78% of average.
• Light precipitation is expected today, followed by relatively dry conditions for the next week.
• Natural flow stayed at 105% of average.
• At an average outflow of 430 cfs, Island Park Reservoir gained 48 ac-ft yesterday and is 91% full, compared with 76% full on average.
• The upper Snake River reservoir system is 77% full, compared with 62% full on average.

Details

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL