Rob Van Kirk, Author at Henry's Fork Foundation

Photo of confluence of Warm River and Henry's Fork

Water Supply and Water Quality Predictions for Summer 2026

The photo above captures the unprecedented situation we face at the beginning of April. The photo, of the confluence of Warm River and the Henry’s Fork, was taken on February 7 and shows the shocking lack of snow we experienced in the watershed all winter as a result of record-breaking warm temperatures. How will the warm winter and lack of snow affect water supply, water quantity, and fisheries? The highlights are below. If you want to read the full 21-page report and see the numbers and graphs, click here. Mean October–March temperature was 5.6°F above average and 2.0° warmer than 2015, which was second warmest in the 1989–2026 record. Natural flow between Henry’s Lake and Island Park Dam was 4.5% higher over the winter than I predicted on October 1, due to much of the winter’s precipitation falling as rain instead of snow. Winter flow out of Island Park Dam averaged 215 cfs, compared with the 1989–2025 average of 349 cfs and an expectation of 170 cfs based on water supply. Snow water equivalent (SWE) peaked on March 16, 27 days earlier than average, at 67% of average, 3rd lowest on record. Natural streamflow is predicted to be the lowest

Water Year 2025: Everything you wanted to know and a lot more!

Every year since 2017, the Henry’s Fork Foundation Science and Technology Team has produced an annual technical report that documents all of our data collection and analysis activities for the year. Water and irrigation year 2025 was a very active year for the team, given one of the hottest and driest summers on record, our 11th year of aquatic invertebrate sampling, and the 20th year of monitoring the rainbow trout spawning run in the Buffalo River. This blog consists only of the report’s summary, but you can download the full 70-page report here. Climate. Mean temperature was 3rd warmest in the 37-year record both for the water year as a whole and for the April–September period. Precipitation ended up at 84% of average for the water year and 66% for April–September, the latter being the lowest in the record. Peak snow water equivalent in 2025 was 92% of average and occurred on April 5, 7 days earlier than average. Drought conditions worsened over the year from “abnormally dry” to moderate/severe drought. Water Supply. Natural flow for water year 2025 was 79% of average, ranking 41st out of the last 48 water years. In the 96-year record for natural flow between

Henry’s Fork Aquatic Invertebrate Trends, 2015-2025

To address angler concerns about decreased hatches, particularly at Last Chance and the upper Ranch, and holistically assess ecological function throughout the mainstem Henry’s Fork, we implemented a statistically rigorous, quantitative study of aquatic invertebrates in 2015. This followed implementation of a watershed-wide water-quality monitoring program in 2014 and prompted subsequent expansion of stream gaging. After our 11th year of sampling in 2025, we had a set of 56 independent observations of macroinvertebrates collected at six different sites on the river over an 11-year period, each accompanied by a full suite of water-quality and streamflow variables. The sites—Flat Rock, Last Chance, Osborne Bridge, Marysville, Ashton Dam, and St. Anthony—represent conditions over the 80 miles of river most popular among anglers. We analyzed invertebrate abundance, five standard community metrics—Shannon’s diversity, EPT taxa richness (the number of mayfly, stonefly, and caddisfly species), Hilsenhoff Biotic Index (HBI), percent non-insects, and percent EPT—as well as the abundance of Pale Morning Duns (Ephemerella sp.), Drunella mayflies (Flavs + Green Drakes), and Spotted Sedge caddis (Hydropsychidae). For each of these response variables, we tested for dependence on distance downstream from Big Springs as predicted by the River Continuum Concept, difference across sites independent of the river

Fish of the Month: Year 11

As it is the afternoon of December 31, I am closing the year with my annual fish-of-the-month blog, this one at the end of my 11th year of catching a fish in my home waters in each month of the year. To spare you the math, that’s 132 consecutive months of catching a wild trout or whitefish (and in some years I’ve fair-caught suckers and shiners, too) within a three-hour drive of my home in Ashton. First fish of 2025, caught on the morning of January 3. As in 2024, I set some constraints on allowable fishing methods to limit my impact on the fish, limiting myself to only two methods of fishing: 1) a single streamer, wet fly or skater fished on a spey rod (in my case, a Loop 11′ 4-weight switch rod), or 2) a single dry fly. I used a couple of different 5-weight rods for the latter, including a Winston 8 1/2 foot, slow-action rod that Mike Lawson gave me as a bonus at the end of the 1984 season at Henry’s Fork Anglers. Last year’s salmonfly shucks underneath a rock in the Warm River to Ashton reach, January 3, 2025. Some things

Estimation of Thurmon Creek sediment load following the drawdown of Silver Lake

In this blog post, we 1) present our turbidity and suspended sediment data, 2) explain our suspended load calculations, and 3) provide some additional information justifying why we think that a substantial amount of bed load was transported into the Henry’s Fork in addition to the suspended load. Since first observing high turbidity in Thurmon Creek and the Henry’s Fork downstream associated with the Silver Lake drawdown in November 2025, HFF’s Science and Technology team has collected turbidity and suspended sediment samples, reviewed the drawdown timeline, and compiled hydrologic data to provide an estimate of the amount of sediment introduced into the Henry’s Fork from this event. By way of background, streams transport two types of sediment: 1) fine material suspended in the water column, and 2) coarse material that moves along the stream bed during high flows. Our measurements of turbidity and suspended sediment concentrations from Thurmon Creek, along with 12 years of background data collected by our water quality monitoring network, allow us to calculate suspended load from this event. Unfortunately, because we did not observe the peak flow event that occurred during drawdown of the lake, we do not have data to calculate bed load. Timeline We

rainbow trout fishing on the Henry's Fork

Henry’s Fork Summer Fishing: Predictions for water supply and water quality in 2025

This time of year, one question is top of mind: what can we expect from the summer fishing season on the Henry’s Fork? Every spring since 2017 I have used a set of computer models to predict water supply, irrigation-system management, water quality, and fishing conditions for the upcoming April–September period. The predictions are intended to provide outfitters and guides, anglers, water managers, water users, and other river stakeholders with an objective set of information that will help them set realistic expectations for the upcoming season. For water managers in particular, the predictions are intended to help fill water rights, meet system-wide objectives, and optimize reservoir carryover as efficiently and precisely as possible. This year’s predictions are presented in three sections: water supply, irrigation-system and reservoir management, and water quality/fishing experience. Here are the key points. If you want the full report, with all tables and graphics, you can view that here. Water Supply Natural streamflow over the period April 1—September 30 is predicted to be 91% of the 2001–2024 average: 83% in the upper Henry’s Fork subwatershed, 95% in Fall River, and 94% in Teton River. For comparison, last year’s April–September natural flow was 92% in upper Henry’s Fork,

Behind the Scenes of HFF’s Daily Water Report

What is HFF’s Daily Water Report? After the severe drought of 2016, which resulted in what is still the poorest water quality we have recorded in 11 years of monitoring at Island Park Dam—as well as the lowest reservoir drawdown since 2007—HFF started laying the scientific foundation for what we would eventually call “precision water management.” In its first seven years, that collaborative program has decreased drawdown of Island Park Reservoir by an average of 23,941 ac-ft and increased winter flow by an average of 100 cfs. See blog posts summarizing water year 2024 and the winter of 2025. One of the centerpieces of the precision water management program is the daily water report, which I first issued to a small group of water managers and water users in early 2017. The daily email distribution list has grown to over 370 subscribers, which include water users, water managers, anglers, fishing outfitters and guides, local journalists, scientists, nonprofit colleagues, weather enthusiasts and others. What goes into the report? Every day, we run a set of computer code that automatically downloads and compiles around 220 pieces of daily climate and water data from a variety of sources, including our own stream gages.

Island Park Winter Flow in 2025: How did we do?

Looking downstream from Island Park Dam on January 6, 2025 after a fresh snowfall. How did Island Park winter flow shape up in 2025? Winter flow in Island Park refers to the December–February (“winter”) period critical for survival of juvenile rainbow trout immediately downstream of Island Park Dam (primarily in Box Canyon), a period of time that ended last Friday. So, if you missed the daily water report in which I analyzed winter streamflow at Island Park Dam and downstream through Box Canyon, I share the results below. Beyond just digging into winter flow operations in 2025, I also share answers to questions like: Why is winter flow so important? What about low flows in the fall? What about the glory days? What role does hydropower play? Why is precision management good for winter flow? What does the future hold? This blog post is long—about a 15- to 20-minute read-time—I recognize that. But I have been working on this topic for 30 years and wanted a place to share everything we know in one place about the role of winter flow in producing trout for the Box Canyon and Ranch fisheries. I encourage you to read the blog post in

How Much Snow Does Henry’s Fork Need for Average Streamflow?

And what does “average” mean, anyway? Now that we are about 75% of the way through the snow accumulation season, we have enough information to make predictions of water supply for the upcoming April–September 2025 season. A water report reader earlier this week suggested that I calculate probabilities of reaching average streamflow from where we currently stand (as of February 20). Thank you for the suggestion—here are the results! A little background information Let me first say the terms “water supply” and “natural streamflow” mean the same thing: the total amount of streamflow doled out to the river system by the watershed from snow, rain, and groundwater springs. Management such as reservoir storage and delivery and irrigation diversion determine the actual amount of streamflow in a reach of river at any given time, but natural flow is independent of management and is the finite amount of water we have to work with. Second, the depth of snow on the ground does not determine water supply for the spring and summer. How much water is in the snow determines spring and summer water supply. That’s why I report snow water equivalent (SWE). SWE is the depth of water obtained from the

Water Year 2024 Technical Report

As most of you know, I started fishing the Harriman Ranch reach of the Henry’s Fork in 1977. I worked for Henry’s Fork Anglers from 1981 through 1987 and fished the Box, Last Chance, and Ranch all summer during those years. I was literally behind the counter at Henry’s Fork Anglers in 1984 while the founders of what would become the Henry’s Fork Foundation were meeting at Joan and Jim Lansche’s cabin. They founded the organization because there were tangible threats to the river—most notably hydroelectric power developments proposed at Island Park Dam and Mesa Falls. There were also other visible sources of degradation, including livestock grazing along the streambanks, at the same time as the fishing was still great. Although I had many great years of fishing the Henry’s Fork back then, nothing could compare with 1984, when I caught two rainbow trout in the 25–26 inch range within two weeks of each other, one in the Box and one in the Ranch. But by the summer of 1985, anglers were starting to report declines in the fishing experience, and by 1987—heading into what would be the first multi-year drought in nearly 20 years—anglers were genuinely worried about the

Ten Years of Aquatic Insect Data from the Henry’s Fork: What have we learned?

To address angler concerns about decreased Henry’s Fork hatches, particularly at Last Chance and the upper Ranch, and holistically assess ecological function throughout the mainstem Henry’s Fork, we implemented a statistically rigorous study of aquatic invertebrates in 2015. This followed implementation of a watershed-wide water-quality monitoring program in 2014 and prompted subsequent expansion of stream gaging. The result to date is a unique data set of 50 independent observations of macroinvertebrates collected at six different sites on the river over a 10-year period, each accompanied by a full suite of water-quality and streamflow variables. The sites—Flat Rock, Last Chance, Osborne Bridge, Marysville, Ashton Dam, and St. Anthony—represent conditions over the 80 miles of river most popular among anglers. We analyzed invertebrate abundance, five standard community metrics—abundance, Shannon’s diversity, EPT taxa richness (the number of mayfly, stonefly, and caddisfly species), Hilsenhoff Biotic Index (HBI), percent non-insects, and percent EPT—as well as the abundance of Pale Morning Duns (Ephemerella sp.), Drunella mayflies (Flavs + Green Drakes), and Spotted Sedge caddis (Hydropsychidae), three species of interest to anglers. For each of these response variables, we tested for dependence on distance downstream from Big Springs as would be predicted by the River Continuum Concept, difference

Fish of the Month: Year 10

The fish-of-the-month tradition started decades ago with my fishing buddy Tom Grimes, who has guided for Henry’s Fork Anglers all of those decades. I’ve had a couple of good multi-year runs over the decades, but this one beats them all…120 consecutive months!