Henry’s Fork

Henry’s Fork, May 11th, 2024

The Henry’s Fork continues to offer the most consistent fishing of any area stream. Good caddis, BWO, and midge activities are reasons for great top water fishing not only on the lower river, but on the river above. Here the Last Chance area and above Coffee Pot rapids are good areas to try. For streamer and nymphing enthusiasts, Box Canyon is worth a try using streamers and fly rod jigs.

Here is some encouraging water quality information from Dr. Rob Van Kirk’s Henry’s Fork drainage SWE report filed yesterday.

Water Quality

As good as water quality was on Wednesday, it was even better yesterday. Water temperatures warmed just a hair, putting them within the optimal range for development of rainbow trout eggs and fry in all river reaches. Increased sunlight yesterday resulted in higher photosynthesis than we have seen in a week, increasing dissolved oxygen watershed-wide. Turbidity continued to drop yesterday, although that trend will be reversed today as snow begins to melt. I expect the highest increases in turbidity to occur downstream of Robinson Creek and Fall River, which are the two tributaries that will respond the most to mid-elevation snowmelt over the next week. Hatch timing is a day behind average at most locations after slowing down over the past five days. However, I expect aquatic insect development to accelerate a little as temperatures warm, putting it back at average to a day or so ahead of average by the end of next week. That means upcoming springtime hatches—including salmonflies and March Brown mayflies—should be right on time. 

Henry’s Lake, May 4th , 2024

Ice is retreating from the lake. The best time for early season fishing is when and where the ice is not far out from the shoreline. Leech and streamer patterns are good choices for action.

A request to help determine Henry’s Lake fish population and physical condition is below.

From Idaho Fish & Game – The ice is coming off the lake fast, and with that comes the beginning of our annual gillnet survey.

 When: We need help for the next two weeks. Looks like we need two volunteers a day to meet us at the Henry’s Lake Hatchery at 8:00 AM each morning. We can provide a truck and carpool up to the lake.

Description:  : The gill net operation will consist of picking fish out of the nets, count fish species, and collect any samples the biologist needs. The picking is the time consuming and can be the smelly part.

What to Bring: Please bring waders(if you have them), a rain jacket & pants(works best). The nets are wet, so waterproof clothing, or ‘work clothes’ is a must and layers to be comfortable in temperatures ranging from 25-70 degrees. Gill net catch rates vary, so working up nets can potentially take several hours and I would suggest packing Snacks, lunch and drinks.  

 Physical Demands: Weather can vary in Island park . Not a real physically demanding job but there is some bending/stooping/kneeling  and hand dexterity to remove fish from nets.

Please click the link to see what days are available. Then email me dates and contact information so I can add you to the schedule.  

Gerren B. Steel

Volunteer Services Coordinator

Idaho Department of Fish & Game

Work: 208-535-8039

Cell: 208-850-7576

Henry’s Fork, May 4th, 2024

Flow is down throughout the river thanks to our recent surprise snow storm (maybe more to come next week), So note what Dr Rob Van Kirk says below about development of aquatic insect growth in his water quality discussion below.. Nevertheless the lower river continues to offer the best stream fishing in the area with great BWO, mother’s day caddis, and midge activity bringing trout up from the bottom. If water quality stays decent and warms a bit, stonefly nymphs will soon wake up. All boat launch locations on the lower river are open.

Headlines from Dr. Rob Van Kirk’s SWE Report for the Henry’s Fork Drainage Filed Yesterday, May 4th

• Another cool, showery day kept water-year total precipitation at average and kept SWE constant at 83% of this season’s peak, compared with 87% of peak on average.
• Very cold, wet weather is expected Sunday–Wednesday, which will add snowpack and likely put SWE near average for the date by the middle of next week.
• Natural flow dropped for the fourth consecutive day and was 83% of average yesterday.
• Water temperatures increased a little yesterday but were still below average, continuing to slow aquatic organism development.

Water Quality 5/3/ 24

Water quality remains very good in all river reaches, as dissolved oxygen concentrations are high and turbidity continues to drop after last week’s peak streamflows. Water temperatures were a hair warmer yesterday than on Wednesday but still below average. Yesterday’s temperatures were generally below the optimal range for development of rainbow trout eggs and fry, which is not harmful but just slows development. Similarly, aquatic insect development continues to slow, as I had predicted at the end of last week. Current hatch timing is within a day of average at most locations but will drop to a day or two behind average by the middle of next week.

In absence of a managed freshet flow out of Island Park Reservoir, sediment mobilization and transport out of the Island Park-to-Pinehaven reach has been below average so far this spring, despite streamflow last week that was almost as high as last year’s managed freshet. In fact, yesterday’s net export of sediment from the reach was the lowest for the date in the 8 years we have measured that quantity carefully. There are two primary reasons for that: 1) there is relatively little fine sediment in that reach to transport this year after last year’s highly successful springtime freshet and subsequent low export of sediment out of the reservoir last summer, and 2) as we learned from last year’s freshet compared with previous freshets, rapid increase in outflow mobilized much more sediment than gradual increase, even if the magnitude ended up about the same. I expect relatively low sediment export rates to continue throughout the remainder of the period before aquatic vegetation growth really gets underway.

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, April 27th, 2024

The lower river offers the most consistent and likely the best fly fishing in the region. Mother’s Day caddis, BWO and midge activities are resulting in excellent top water fishing. Days with little wind are best. Streamer fishing also continues to be good during low light conditions. On the upper river the Last Chance area features some good midge hatches with a few BWOs showing, but weather can be difficult. Flow in the river is increasing as the run-off season is getting underway. The biggest impact will be on the river below the Fall River confluence downstream to the South Fork confluence.

Headlines 4/26

Water Quality information from Dr. Rob Van Kirk’s Snow Water Equivalent Report for the Henry’s Fork Drainage Filed Yesterday

Water quality remains very good in all river reaches and continues to show influence from rapid snowmelt watershed-wide. Conductivity continues to drop at all locations, indicating a large influx of relatively pure surface water from snowmelt. Turbidity continued to drop from a peak earlier in the week at Flat Rock but is still increasing at all other locations due to increased streamflow. However, current turbidity values are within the range typically observed during periods of snowmelt. Water temperatures were a little cooler yesterday than they were earlier in the week, and aquatic insect development is within two days of average at all locations. I expect hatches to slow a little over the next few days, as cloudy and cooler weather keeps water temperatures a little below average.

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, 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.

• 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.

.

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