Current and Upcoming Projects

Duck Creek Fish Passage Project: This one has been in the works for awhile, but was finally completed this fall. On Duck Creek, a dilapidated diversion headgate was causing problems for fish passage. With funding help from the U.S. Fish and Wildlife Service and Henrys Lake Foundation, we were able to replace that headgate and install an engineered riffle that will allow fish to move upstream and downstream at-will. The contractors who did the work noted that they’ve never seen a project area populate with fish so quickly after installation! 

Lower Targhee Creek: Over the past few years, IDFG, Henrys Lake Foundation, the landowner, and other partners have been working diligently to plan, design, fund, and implement a large-scale restoration project on lower Targhee Creek. Targhee Creek is the most important tributary to Henrys Lake, supporting spawning runs and providing critical thermal and oxygen refugia during the heat of summer and cold of winter. We’ll be breaking ground on this project in 2026, and it will involve the reconnection of a historic channel of Targhee Creek providing additional YCT spawning and rearing habitat, as well as habitat restoration activities in mainstem. Projects like this with so many passionate and invested partners are how we move the needle for the Henrys Lake fishery!

Ask a Biologist

At the end of each newsletter, I like to have an “Ask a Biologist” section where I can help answer/explain a timely and important question I receive about Henrys Lake or the surrounding watershed. Please send me any relevant questions you may have! My email is Nathan.Tillotson@idfg.idaho.gov. 

Question: Why are hatchery-stocked fish not surviving consistently in Henrys Lake and what is IDFG doing about it?  

Answer: 

As to the “why”, we’ve spent considerable effort digging into this exact question. Unfortunately, our stocked fish are incredibly difficult to get our hands on between the time of stocking and when they show up in our gillnet survey at age-2. Without being able to survey them consistently and effectively during that life stage, it’s difficult to identify the exact causes of mortality. However, we’ve narrowed it down to two leading theories that are not mutually exclusive. Water quality and predation. 

Water quality is a tough one because we don’t have the ability to significantly change things like water temperature, dissolved oxygen, or harmful algal blooms on Henrys Lake. If lake conditions at the time of stocking are poor, then it’s not surprising that a large portion of our hatchery fish don’t survive long after leaving the truck. Predation is similarly challenging because we know growth of adult trout in Henrys Lake is correlated with our stocking numbers on any given year. Our bigger trout are taking advantage of stocked fingerlings as soon as they leave the truck. We believe this problem was particularly impactful with our HYB stocking in recent years. From 2019-2024 we stocked HYB in June rather than our normal program of stocking all species in September. Adult trout were able to take disproportionate advantage of our HYB since they were stocked so much earlier and because we stock considerably fewer HYB than YCT. 

Fortunately, we do have some tools in our fisheries toolkit to try to address these concerns. Stocking strategy evaluations. While we can’t meaningfully change Henrys Lake water quality by flipping a switch, and neither can we convince our adult trout to not gobble up as many hatchery fingerlings as they can stomach, we can use the information available to give our hatchery fingerlings the best chance for survival by changing how we stock fish. Not only have we returned our HYB stocking timing to September with the rest of the fish, but we are currently evaluating two different stocking strategies to address water quality and predation concerns. 

In 2024 and 2025, we began stocking a portion of YCT fingerlings with known genetic signatures in the tributaries to Henrys Lake. Even if lake conditions aren’t favorable for fingerling survival, conditions in the tributaries should be much better from a water quality perspective. Further, stocking fingerlings in the tributaries should allow these hatchery fish to get their bearings in a place with fewer predators before out-migrating to the lake. In the coming years, we’ll be able to compare relative survival of lake-stocked fish to tributary-stocked fish in the gillnet catch. 

The second major stocking strategy study is a size-at-release evaluation for our HYB. However, this project was more than we could accomplish on our own. Funding and logistical challenges associated with existing hatchery space limited our ability to accomplish this in-house. Because of the generosity and savvy of the great folks at the Henrys Lake Foundation, we were able to team up to make it happen. With their help, we secured space at a private hatchery to rear some Henrys Lake HYB to larger sizes prior to stocking. This study will involve stocking one group from the private hatchery at the same size and time as the rest of the HYB (which happened in September 2025), while the other group will be held over-winter to be stocked in May 2026 at ~7 in. The first winter of a fish’s life is when it’s most likely to die, so holding these fish in a controlled hatchery environment overwinter should allow elevated survival rates as compared to fish stocked prior to their first winter. Additionally, these larger HYB should be less vulnerable to predation by adult trout, further increasing their odds of survival. Each group from the private hatchery will be marked with a pelvic fin clip so we can compare survival among groups, but you likely won’t catch them until they get large enough by the end of 2026 or early 2027. The picture below is from our first fin clipping effort this past fall, but we’ll be doing another fin clipping in Spring 2026. These are large efforts, so please reach out if you’d like to be involved!