Fishing Reports

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