What’s Hatching on the Henry’s Fork?

Home » Blog » What’s Hatching on the Henry’s Fork?
A salmonfly nymph and newly-hatched adult sit on a blade of grass alongside the river. Text reads "What's Hatching? (Or Not)"

In this blogpost, learn about what we know, what we don’t know, and how you can help by reporting the hatches you see (or don’t see) every time you visit the river. Check out the Henry’s Fork Hatch Survey today at tinyurl.com/hfhatchreport.

What We Know

The Henry’s Fork Foundation has been monitoring aquatic macroinvertebrates (insects) at multiple locations since 2015. Each March (normally on St. Patrick’s Day), HFF and a team of entomologists from River Continuum Concepts head out to the Henry’s Fork to scrub rocks and collect bugs from the river-bottom for expert identification and robust analysis to answer questions like:

  1. How many bugs are there? (Abundance)
  2. What kind of bugs are there? (Species Diversity, Richness, Composition)
  3. How have the bugs changed through time?

As scientific river detectives, we pair aquatic insect numbers with water quality and streamflow data and run it through rigorous statistical analysis to better understand changes to the macroinvertebrate community. What have we learned so far? A decade of data show that aquatic invertebrates on the Henry’s Fork are largely happy and healthy. When it comes to Pale Morning Duns, we are seeing declines in abundance at Flat Rock and St. Anthony, but no trends one way or the other at Last Chance, Osborne, or Marysville. Overall, our bug metrics are as good as or better than any other popular western trout stream.

What We Don’t Know

But anglers are reporting wonky, pleasantly unexpected, or downright disappointing hatches—in stark comparison to the consistent hatches Henry’s Fork anglers have longtime counted on in planning their fishing day or fishing vacation. What’s up with that? How can we have strong, stable insect populations and unreliable, inconsistent hatches?

There are so many possibilities. These river bottom-living bugs may be hatching at different times of day or maybe even multiple times per year. Maybe it’s about weather or water temperatures or streamflow. We don’t know. And we need your help.

At HFF, we can’t be everywhere on the river all the time. But we can just about get there by relying on all of you, the Henry’s Fork community, to be our eyes with every trip to the river—whether there’s a rod in your hand or not.

The Henry’s Fork Hatch Survey

After every river visit, please fill out our survey. Tell us when you visited the river, where you visited the river, and what you saw (even if you saw nothing at all).

This is a numbers game. With enough observations, you can help us build a more complete picture of the river and contribute to innovative, science-based river conservation. Add the Henry’s Fork Hatch Survey to your river routine and invite your fishing buddies to do the same. It takes less than 2 minutes.

Extra Info:

  • Don’t let the size of the hatch prevent you from reporting. If you see bugs hatching, whether it’s a whole bunch or just a few, we want to hear from you.
  • If you need a bug identification refresher, don’t worry—the survey provides pictures (courtesy of some generous photographers, thank you!). We’ve also put together an identification guide together for reference.
  • If you feel skeptical about reporting your observations and are concerned with having all kinds of anglers on your favorite river reach, we get it. Be assured: we will not broadcast your observations in real-time. This is purely for science, not for social media. All observations will be summarized for seasonal reports. Although I (Christina Morrisett, author of this blog and lead scientist on this survey) might email you to verify an observation because of an entry typo or unexpected sighting, your observation will be anonymized for inclusion in our handy dandy scientific spreadsheet.

Your input is valuable. Thank you for your contributions so far and let’s keep it going!

 

Facebook
LinkedIn
Pinterest

Recent Posts

Drone image of Island Park Dam, where a low lake level is visible on the right (above the dam) and turbid outflow is visible on the left (below the dam).
Water Quality
Christina Morrisett

October Forecast for Water Quality in Island Park

Drone photo of Island Park Dam taken on September 9, 2026 Looking Back on September September brought lows and highs to Island Park. Island Park Reservoir started September at 29% full and quickly fell to a low of 12% full on September 19. The rapid drawdown of the reservoir was the result of managers needing to move water downstream to American Falls (to irrigate farms in the Magic Valley with senior water rights). Such low

Read More »
Water Quality
Christina Morrisett

Breathing Easy: Oxygenation in Island Park Reservoir

This story was written by Audrey Hunter (2026 intern) and was originally published in the Fall 2026 Newsletter. It’s no secret that late summers on Island Park Reservoir haven’t been in perfect conditions in recent years. Warm, turbid, algae-filled water plague reservoir recreationists while diminishing water quality downstream. Cyclical algal blooms decrease water clarity and create less-than-ideal circumstances for the reservoir’s flora and fauna. What’s the solution? HFF’s DIRTT Plan. In-Reservoir Oxygenation Nutrients released from

Read More »
Drone image of Island Park Dam taken on September 9, 2026
Frequently Asked Questions
Christina Morrisett

Island Park Reservoir Outflow Plan (Updated 9/16)

Drone photo taken on September 9, 2026 The Henry’s Fork Drought Management Planning Committee met on Wednesday, September 16 2026 to develop an updated reservoir management strategy. Downstream of the Henry’s Fork watershed, lower-valley irrigation demand over the rest of the season is anticipated to be slightly lower than projected last week, so Island Park Reservoir and Grassy Lake (in the Fall River drainage) do not need to deliver any more water out of the

Read More »
Frequently Asked Questions
Jasper Davis

FAQ: Island Park Reservoir Fall 2026 Strategy

This year has brought the Henry’s Fork watershed an extraordinary water-supply challenge. Natural flow is exceptionally low, and Island Park Reservoir is ending the summer at a near-record low level. But there is another important part of this story: we knew these conditions were coming, we planned for them, and water managers are managing the water we have as carefully as possible. HFF is one of the 6 official signatories to the Henry’s Fork Drought

Read More »