In honor of HFF’s 35th Anniversary, each week in March and April we will share significant findings or key facts we’ve learned about the river over the past 35 years. Get ready for a crash course in Henry’s Fork trout habitat, fish passage, macroinvertebrates, hydrology, Island Park Reservoir, water quality, economic value of fishing, and water management.


35th Anniversary — Lessons Learned

PART 1:  Ranch Habitat

A great deal of research was conducted on fish habitat, especially in the Railroad Ranch reach, to answer the question “What limits the trout population and how can we increase it?”. Much of this research was conducted between the mid-1980s and late 1990s by graduate students of Dr. Jack Griffith of Idaho State University, with additional research conducted in 2013-2014 by graduate student Zach Kuzniar. What follows is a very simplified summary of five key findings related to Ranch habitat. To learn more about each topic or research effort, follow the links provided or visit us at the HFF Community Campus for additional resources.


1.  By the mid-1990s, research identified winter survival of juvenile rainbow trout as the single factor limiting the population in the reach from Island Park Dam to Hatchery Ford. (Gregory, 2000; Meyer, 1995; Mitro, 1999)


2.  The only real winter habitat is in the Box Canyon because macrophytes (rooted aquatic plants) don’t provide winter cover, they senesce and disappear in the winter. (Griffith and Smith, 1995; Meyer, 1995).


3.  Higher flows below Island Park Dam lead directly to an increase in the amount of bank habitat, which leads directly to an increase in the number of young trout that survive the winter. (Contor, 1989; Mitro, 1999; Angradi and Contor, 1989)


4.  Putting permanent structures like Christmas trees or “trout hotels” in the river were ineffective because they simply filled up with sediment. Macrophytes do not have that issue because they trap sediment and then release it when they senesce so it can be flushed away. (Gregory, 2000; Henry’s Fork Foundation Newsletter, Winter 1995)


5.  Physical habitat structure in the Harriman reach during the fishing season is provided by rooted aquatic plants, which increase water depth at a given streamflow rate. Also, adult rainbow trout seek deeper water, all other factors being equal. (Kuzniar, Van Kirk, and Snyder, 2017)




Angradi, T., and C. Contor.  1989. Henry’s Fork fisheries investigations. Project F-71-R-12, Subproject III, Jobs 7a and 7b. Idaho Department of Fish and Game, Idaho Falls.

Contor, C.R. 1989. Diurnal and nocturnal winter habitat utilization by juvenile rainbow trout in the Henry’s Fork of the Snake River, Idaho. Master’s thesis, Idaho State University, Pocatello.

Gregory, J.S. (2000), Winter Fisheries Research and Habitat Improvements on the Henry’s Fork of the Snake River. Intermountain Journal of Sciences, 6:232-248.

Griffith, J. S. and Smith, R. W. (1995), Failure of Submersed Macrophytes to Provide Cover for Rainbow Trout throughout Their First Winter in the Henrys Fork of the Snake River, Idaho. North American Journal of Fisheries Management, 15: 42-48. doi:10.1577/1548-8675(1995)015<0042:FOSMTP>2.3.CO;2

Kuzniar, Z. J., Van Kirk, R. W. and Snyder, E. B. (2017), Seasonal effects of macrophyte growth on rainbow trout habitat availability and selection in a low‐gradient, groundwater‐dominated river. Ecol Freshw Fish, 26: 653-665. doi:10.1111/eff.12309

Meyer, K. A. 1995. Experimental evaluation of habitat use and survival of rainbow trout during their first winter in the Henrys Fork of the Snake River, Idaho. Master’s thesis, Idaho State University, Pocatello.

Mitro, M. G. 1999. Sampling and analysis techniques and their application for estimating recruitment of juvenile rainbow trout in the Henrys Fork of the Snake River, Idaho. Ph.D. dissertation, Montana State University, Bozeman. 288 pp.