Trout growth is increasing at Chesterfield Reservoir’s fishery

The following is a news release from the Idaho Department of Fish and Game.

CHESTERFIELD – Chesterfield Reservoir in southeast Idaho has been a sought-after destination for anglers for decades. While many anglers enjoy the open water season, this reservoir also supports a popular ice fishery. Ice usually establishes early and extends for the duration of the winter (which can be long in this part of the state).

Chesterfield Reservoir is known for its superb growth and abundance of hatchery-stocked rainbow trout available to the public to harvest. Historically, Utah chub—which are native to the reservoir and spawn in the beaver complexes of the Portneuf River above the reservoir—were believed to limit the performance of rainbow trout. In response, several rotenone treatments were used in the 1990s and early 2000s to reduce Utah chub densities.

However, recent work completed at Henrys Lake in eastern Idaho focused on how Utah chub may impact trout growth, but no evidence of competition was found. An article with this information can be found here.

Chesterfield Reservoir was last surveyed by Idaho Fish and Game in 2001. Given the importance of the Chesterfield Reservoir fishery to the angler community, Fish and Game’s Southeast Region fisheries management team sought out to answer how the reservoir was performing in 2024. This past June, we utilized our standard “lowland lake” methods of gillnets, trapnets and boat electrofishing to sample the reservoir.

What the data shows

A total of 102 rainbow trout were sampled in our survey with an average length of 15.3 inches and 1.8 pounds. These averages have increased since the 2001 survey when rainbow trout averaged 14 inches and 1.5 pounds. The largest rainbow trout captured in 2024 was 22.3 inches and weighed 4.1 pounds! We also captured 89 Utah chub in our sample, which represented 47% of all the fish we sampled. Densities of Utah chub seem to be slightly lower than in 2001, where Utah chub represented 58% of catch. Although Utah chub are still prevalent in Chesterfield Reservoir, it seems rainbow trout are continuing to grow to trophy sizes.

What we did next

Because of the large growth potential for stocked trout, our fisheries management team wanted to increase angler opportunity on the reservoir. Our current annual stocking request from our hatcheries is for 38,400 catchable rainbow trout (12+ inches), split between the spring and fall. In 2024, an additional 21,500 were stocked by our hatchery team, including 216 broodstock fish (donated by Riverence Hatchery) that averaged 7.8 pounds. This should create an outstanding ice fishery this winter and translate into the open water fishery of 2025.

Report tags to help with fisheries management

At Chesterfield Reservoir, we also placed T-bar anchor tags into trout to improve fisheries management by gaining information on angler catch and harvest rates. Reporting these tags help biologists understand harvest, survival, growth, and movement. If you catch one of these fish, report it to the Tag! You’re It! website or call 1-866-258-0338.

For more information about the management of Chesterfield Reservoir or other southeast Idaho fisheries, please contact the Southeast Region Idaho Fish and Game office in Pocatello at 208-232-4703.

Two people in a boat floating on a very blue water body, handling fish in a large net
Fisheries staff from Idaho Fish and Game’s Southeast Region sampled fish in Chesterfield Reservoir in June 2024 in an effort to better understand this reservoir’s performance as a fishery.

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