Henry’s Fork

Henry’s Fork, May 30th, 2023

The big stone flies are out along the river from Ashton Dam down to Chester backwaters, but the same with fly fishers, wading and boating. It is likely the big bugs are also out in lower Cardiac Canyon just above the Warm River confluence. If you are looking to get away from crowds, here are a few locations that will help do so.

Park at the old Bear Gulch Ski area and walk down the service road to the river. When you arrive at the river, walk upstream for the best fishing.

From Riverside Campground walk downstream on the marked trail. The trail is adjacent to the river going almost to the west side of Hatchery Ford. The last out take for boats before Cardiac Canyon is on the east side of the river at this point. This place can also be reached by taking the West Hatchery Ford road from U. S. Highway 20.

Headlines from Dr. Rob Van Kirk’s Snow-Water Equivalent Report Compiled Yesterday

• Temperatures were average over the holiday weekend, slowing snow melt a little; nonetheless, SWE is 36% of this year’s peak, compared with 44% of peak remaining on average.
• Natural streamflow has dropped over the past four days to 121% of average.
• At an average outflow of 1,349 cfs, Island Park Reservoir gained 122 ac-ft/day over the weekend and is 98% full, close to average for the date. Expect continued small outflow changes to manage fill.
• The upper Snake River reservoir system is 82% full, compared with 79% full on 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, May 26th, 2023

As of yesterday, none of the big stone flies are flying and egg laying around the river between Ashton Dam and Chester. Presenting big stone fly nymph, rubber leg, woolly bugger types, streamer and San Juan worm patterns are likely to bring the best chances of fishing success up and down the river for a while.

In the Island Park area, Buffalo and Riverside campgrounds will be open for the Memorial Day weekend. Some loops within each may be closed in order to dry out.

Henry’s Fork, May 23rd, 2023

Big stonefly nymphs are migrating in the river from Cardiac Canyon on downstream, but if any are flying and egg laying, their numbers are small enough that trout are not yet attracted. Aquatic insect activity is several days behind across the entire Henry’s Fork drainage. Here is an item from Rob Van Kirk’s SWE report filed yesterday concerning aquatic insect activity in the drainage: “Timing of aquatic insect hatches is running around 2-6 days later than average in the upper watershed and 4-11 days later than average in the lower watershed. Given continued snow melt, increased cloudiness, cooler temperatures, and rain, I do not expect hatch timing to catch up to average any time soon.”

Back country road and campground openings are also behind for this time of the season. With Memorial Day weekend coming up, the Ashton/ Island Park Ranger District office will have the best information on road and campground openings/closures.

Henry’s Fork, May 20th, 2023

Any day now the giant then golden stone flies will be out along the lower river from Cardiac Canyon downstream to the Chester backwaters. Until these emerge, then fly and begin egg-laying activity, presenting nymph patterns of these will be effective. Caddis activity also abounds along this stretch of river. Discolored water persists from Warm River to Ashton Reservoir.

Henry’s Fork, May 16th, 2023

Forget about fishing the Warm River to Ashton section for a while. Robinson Creek and even Warm River (right now a run-off stream thanks to Island Park snow pack) are putting in cold, discolored water. Nevertheless, big stonefly nymphs are moving, and as we close in on the end of the month will be out and hatching along the lower river. Mother’s Day caddis remain along the lower river and best to encounter fish feeding on them is below Ashton Dam. Avoid using the Ora Bridge boat launch to minimize road damage until water level in the gravel pit drops.

Headlines from Dr. Rob Van Kirk’s Water Supply Report filed yesterday for the Henry’s Fork Drainage.

• Temperatures and snowmelt were well above average yesterday; 71% of this year’s peak snowpack remains, compared with 66% on average.
• Natural streamflow is 140% of average.
• At an average outflow of 1195 cfs, Island Park Reservoir gained 2000 ac-ft yesterday and is 94% full, compared with 96% full on average.
• Although 95% full physically, the three reservoirs in the Henry’s Fork watershed are 57% full on paper, as the American Falls 1921 right is still being filled.

Henry’s Fork, May 13th, 2023

Flow is up with colder water throughout the river ( especially below Fall River and Warm River-Robinson Creek confluences) making for slower top water fishing even though BWO and Midge activity is good. Mother’s Day caddis are active in places. Streamer fishing can be productive when concentrated during low light periods and at out-of-direct-sunlight areas. Pattern choice is less important than understanding these conditions.

Stonefly nymphs are beginning to migrate and therefore becoming more available as a food form for trout. That’s another reason for slower top water fishing. Fish use less energy to feed along the river bed than rising to the surface. So as we move later in May, stonefly nymph patterns become more important in your fly box until adults appear.

Henry’s Fork, May 9th, 2023

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

• Temperatures and snow melt were lower yesterday than earlier in the week but still above average.
• Natural stream flow increased yesterday to average but is likely to level off today, depending on location and amount of rainfall.
• At an average outflow of 695 cfs, Island Park Reservoir gained 421 ac-ft yesterday and is 86% full, compared with 93% full on average.

Water quality

Turbidity continues to increase across the watershed in response to snow melt and increasing stream flow. Turbidity is particularly high right now in Fall River and other tributaries such as Robinson Creek. Water temperatures dropped back to average yesterday at all locations except Island Park Dam, where ice cover has kept temperature at 39 degrees F. Our water quality data show no signs of open water on the reservoir yet. Ice melted last year on May 6, the latest date of ice-off we have observed since installing our water quality instruments in 2014. This year’s ice-off date is likely to be 4-6 days later than that

.

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, May 6th, 2023

Ground water flooding impacts access at the Vernon Bridge.

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

• The month of April was cooler and slightly drier than average.
• Watershed SWE peaked last Monday, at 119% of the average annual peak; 94% of this year’s peak SWE is still on the ground, compared with 87% on average.
• Natural flow is increasing in response to snowmelt; moderate rainfall is expected later in the week.
• Last week’s freshet exported 321 tons of sediment out of the Island Park to Pinehaven reach, compared with about 30 tons had the freshet not occurred.

Here is some interesting info from Dr. Van Kirk on the effects of the freshet performed for four days in late April.

Over the four days of the freshet operation, 321 tons of fine sediment were exported from the river reach between Island Park Dam and Pinehaven. Based on pre- and post-freshet numbers, we expect that about 30 tons would have been exported over those four days had the freshet not been done. For reference, the average annual net export of fine sediment from the reach over irrigation years 2016-2022 is 650 tons. So, the freshet moved half of the average annual sediment budget in three days. Freshet-related turbidity has dropped to near pre-freshet levels, but now increased stream flow from natural snow melt is increasing turbidity again, especially in the lower watershed.

Meanwhile, warmer water temperatures are accelerating aquatic insect development, although hatch timing remains later than average and even later than last year over the lower watershed. We expect rapidly warming conditions over the next few days, but the cooler forecast for late in the week could slow down progress toward average hatch timing ( His info on aquatic insect hatches helps explain the relatively slow recent fishing on the lower river).

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELLG

Henry’s Fork, May 2nd, 2023

Headlines from Dr. Rob Van Kirk’s SWE report filed yesterday for the Henry’s Fork drainage.

Headlines
• Temperatures and snow melt were well above average yesterday, but current SWE is 10% above the average annual peak and 27% above average for the date.
• Natural stream flow has increased 22% in the past two days and is 72% of average for the date.
• Precipitation over the next week is now forecast to be heavy, with much cooler temperatures.
• My forecast for April-September total natural stream flow is 105% of average for the watershed: 102% in upper Henry’s Fork, 103% in Fall River, and 106% in Teton River.

Henry’s Fork, April 25th, 2023

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

• Precipitation overachieved yesterday, pushing SWE to yet another seasonal peak, at 119.2% of average.
• Dry weather and a warming trend start today, which will greatly increase snow melt across the watershed.
• Island Park Reservoir will start today’s freshet delivery at 91% full and just a few inches below the rubber spillway collar.
• Outflow from Island Park will be increased to 2,000 cfs in four hourly increments this morning.

Outflow will be increased to 2,000 cfs in four hourly increments this morning and held at 2,000 cfs until at least Thursday and most likely until Friday morning. Post-freshet outflow is tentatively planned to be set at 650 cfs, but the exact figure will be determined by inflow rate. Current inflow is around 500 cfs, but I expect that to jump quickly over the next few days to 800 cfs and likely to exceed 1,000 cfs by the weekend. This will impact flow downstream to Ashton Reservoir and has purpose of helping to flush silt from the river bed.

Rob Van Kirk, Ph.D.

Senior Scientist

Henry’s Fork Foundation

P.O. Box 550

Ashton, ID 83420

208-881-3407 CELL