About Wild Trout

Thriving Wild Trout

Studies have demonstrated that wild trout spawn very successfully in the caldera section, particularly in the Box Canyon but also in Last Chance and certain places in the Ranch as well. The river is fully seeded; what limits the population of wild trout is the ability of juvenile trout to survive their first winter. Survival is a function of habitat availability, which in turn is dictated by water.

Adequate water flows make a variety of habitat, in particular along the river’s margins, available to young-of-the-year wild trout. Insufficient winter flows limit juvenile trout habitat, dramatically increasing mortality rates. Other factors, such as water quality, temperatures, or the availability of food are not limiting factors on the Henry’s Fork; indeed, trout grow faster in the caldera section than they do in any other documented stream reach in the state of Idaho. HFF radio-telemetry fish tracking has demonstrated that adult rainbow trout survive the winter well, even under adverse flow conditions.

Wild Rainbow Trout


Rainbow trout were introduced into the Henry’s Fork watershed in the late 1800s. Over the years, successive introductions of rainbow trout gradually replaced the river’s native trout, the Yellowstone cutthroat.

Fish eradication efforts targeting suckers and other non-game fish in Island Park Reservoir (most recently in 1992), and two treatments (1958 and 1966) of the mainstem Henry’s Fork above Mesa Falls and the mainstem and tributaries above Island Park Dam (whitefish) failed to eliminate their intended species but did probably remove virtually all of the “original” introduced rainbow trout stocks, which were subsequently replaced by planted rainbow trout from various sources.

Contrary to rumors, there is no evidence to suggest that the source of either the original stocked Henry’s Fork rainbow trout or those introduced after the 1966 eradication was the famous McCloud River strain from California.

An exception to the wild trout fishery is the limited stocking of hatchery trout that are annually introduced into the Island Park Reservoir and Ashton Reservoir. This has influenced wild trout sections of the river. Unknown numbers of stocked rainbow trout have moved out of Island Park Reservoir and through the dam outlet into the Henry’s Fork over the years. In 1994, Island Park Dam was retrofitted with a hydropower facility that included a fish-screened dam intake. At reservoir levels below 21 percent of capacity, however, water passes through the old, unscreened intake; it is at these low lake levels that fish are most concentrated and, presumably, most likely to move through the dam. Rainbow trout thus continue to be introduced into the river from the reservoir.

Wild Brown Trout

In addition to the wild rainbow trout fishery, the lower river (below Mesa Falls to the confluence with the main stem of the Snake) is now also a prized brown trout fishery. Brown trout were introduced in the early 1980s through the combined efforts of local fisherman and Trout Unlimited to add another quality game fish to the famed waters. In fact, the efforts were so successful that the Idaho state record brown trout was caught on the lower Henry’s Fork by a local angler, named Wes Case, in November of 2008. The fish weighed an impressive 27 pounds 3 ounces.

Wild Cutthroat Trout

The only wild, and native, trout of the Henry’s Fork region is the the Yellowstone cutthroat trout. The HFF is committed to working on Yellowstone cutthroat trout restoration efforts that will return the river’s native trout to habitat in the headwaters of the watershed, provide valuable recreational opportunities, and avoid an Endangered Species Act listing for Yellowstone cutthroat trout. The Foundation is completing an 11-year assessment of the status of the species in the watershed, and working with state and federal fisheries managers to locate suitable sites for cutthroat restorations; one such restoration has already been completed, in Sawtell Creek. The HFF has recently probed into the far reaches of the Henry’s Fork watershed in Yellowstone Park. As a result the HFF was able to document cutthroat populations in tributaries that were unknown to hold native and wild cutthroat trout.

Wild Brook Trout

Brook trout (Salvelinus fontinalis) were introduced into the Henry's Fork watershed in late 1800s. The native range of brook trout includes most of northeastern North America. They are predominantly found in small streams, though occasionally they’re caught in the Henry's Fork. Brook trout are present in more stream miles in the Henry's Fork watershed than any other trout species. They readily compete with the native Yellowstone cutthroat trout and have displaced this cutthroat trout subspecies from most head-water streams. Adult brook trout rarely exceed a length of about 8 inches in the small, cold streams they inhabit in the watershed. However, they do grow quite large in Henry's Lake and the Idaho state record brook trout (8 lb 3 oz, 25.5”) was caught there in 1988.