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Henrys Lake Newsletter - October 2021

Henrys Lake Quarterly Newsletter October 2021

Each year we stock Henrys Lake with three species of trout. We stocked 131,197 sterile Henrys Lake hybrid trout on June 17, 2021. On September 21 and 22, 2021 we stocked 839,388 Yellowstone Cutthroat Trout at ~3” in length and 59,711 sterile Brook Trout at ~5.5” in length.  

That’s a total of 1,030,296 Trout stocked in 2021

Figure 1: The number of trout by species stocked into Henrys Lake from 1991 to 2021 where YCT= Yellowstone Cutthroat Trout, HYB= Hybrid Trout (Yellowstone Cutthroat x Rainbow Trout), and BKT= Brook Trout.

Harmful algal bloom on Henrys Lake

Eastern Idaho Public Health and the Idaho Department of Environmental Quality (DEQ) issued a health advisory for Henrys Lake and the shoreline of upper Island Park Reservoir on September 9, 2021. This advisory was issued due to the presence of harmful blue-green algal blooms and is still in place as of October 4, 2021. This advisory will be lifted in the event that two samples from the lake, collected one week apart indicate toxin levels are below the safe threshold.

For more information on this advisory and who to contact please click here. Once the advisory is lifted a news release will be issued by the entities above and shared on our Idaho Fish and Game Upper Snake Facebook page.

What is a harmful algal bloom?

Blue-green algae also known as cyanobacteria are microscopic bacteria that occur naturally in Idaho's lakes and rivers. Cyanobacteria obtain energy through photosynthesis and in the right conditions, which most commonly includes increased water temperatures, abundance of nutrients and stagnant water can grow, or bloom, to high densities. This most often occurs in later summer or early fall and is common across the state. Cyanobacteria blooms can be harmful by creating mats on top of the water which block sunlight, or use up oxygen and nutrients that are needed by other organisms to live. Cyanobacteria can also create cyanotoxins which can be harmful to people, pets, and wildlife. Exposure to cyanotoxins can cause health effects ranging from mild skin irritation to death and is particularly harmful to dogs and other animals. As such it is important to keep yourself, children, and pets out of the water, avoid water sports, and do not drink the water as boiling will not remove cyanotoxins.

Is it safe to eat fish?

To better understand the risk of eating fish from waterbodies affected by a harmful algal bloom, please visit the Center for Disease Control’s website at Avoid Harmful Algae and Cyanobacteria | Harmful Algal Blooms | CDC. Additional information can also be found at Idaho Department of Health and Welfare's website in the Harmful Algal blooms section at the bottom of the page.

Upcoming November to January

1. Electric fences: Each year our staff maintain electric exclusion fences that keep livestock away from the shoreline of Henrys Lake and from Henrys Lake tributaries. During the fall, once livestock have been relocated south for the winter we winterize these fences. This includes removing our electrical equipment and lowering the fence to the ground to decrease the potential of animals getting entangled with fence wire through the winter.

2. 2021 Ice Fishery creel: Each winter our staff conduct interviews with anglers to gather angler effort, catch, and harvest information during the Henrys Lake ice fishery. Specifically, we collect number of hours fished, number and species of fish caught, length of fish data, as well as some angler opinions about the fishery and their fishing experience.

3. Winter dissolved oxygen surveys: Each winter we measure the amount of dissolved oxygen in the water throughout the lake under the ice. The amount of oxygen in water is crucial to the survival and health of fish. When oxygen levels decline, fish can become stressed or die. The more oxygen there is available in the water column the better the health and survival of fish. We monitor the dissolved oxygen at 5 sites around the lake each December and January. We use these data to predict the amount of oxygen in the water through the remainder of the winter and early spring, as this information will help describe the condition of trout returning to the hatchery to spawn and the condition of the eggs which affects survival of eggs after spawning.

Ask a Biologist At the end of each newsletter we will have a section addressing any questions you may have. Please send any new questions to

Q: Are the regulations on Henrys Lake going to change for 2022?

A: Thank-you to everyone who commented on the Henrys Lake season setting proposals. The Idaho Fish and Game Commission is scheduled to discuss the fishing season setting proposals across the state during the November commission meeting on November 15-16 2021 in Lewiston, ID. It is during this meeting that the public comments and proposals for Henrys Lake will be discussed. The commission is then scheduled to make a decision on the fishing regulations for implementation starting January 2022.

Our next quarterly newsletter will be sent out in January 2022 so stay tuned!

If you have any questions, thoughts or concerns please contact the Henrys Lake Biologist Jenn Vincent at

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