HFF Blog

35th Anniversary -- Lessons Learned. Part 1: Ranch Habitat

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

Water Supply Improves in January

Photo of moonset on snowy morning
  • January climate stats: 1 degree F above average temperature, 89% of average precipitation, and 83% of average snow water equivalent (SWE) accumulation.
  • February 1 water-year totals: 85% of average precipitation and 77% of average SWE.
  • February has better than even odds of being colder than average, and has started out very wet.
  • Island Park Reservoir has been steady at 88-89% full for the past two months. Outflow has averaged 520 cfs.

Yellowstone Cutthroat Trout Management on the South Fork Snake River


  • Fall IDFG surveys estimated Rainbow Trout and Rainbow x Yellowstone Cutthroat Trout Hybrid abundances nearly doubled in 2018 and set a record high of 3,073 fish/mile in the Conant index reach.
  • If left unmanaged, Rainbow Trout would likely hybridize and out-compete native Yellowstone Cutthroat Trout in the South Fork Snake River.

Fish of the Month: Year Four

Photo of Brown Trout.

In January of 2015, I started a new run of "fish of the month," a tradition I started years ago with long-time friend Tom Grimes, who is a guide at Henry's Fork Anglers. The idea is to catch a wild trout or whitefish every month of the year in our local waters, the streams and lakes of Montana, Wyoming, and Idaho in the Yellowstone region. My previous record was 55 months, from July 2004 to January 2009. Five academic years spent in California broke that streak, but I'm four years into the current one. How did 2018 turn out?

After dry December, snowpack only 70% of average

Photo of Brown Trout.
  • Precipitation for the month of December was only 57% of average.
  • As of January 1, water-year precipitation was 84% of average, and snow water equivalent was 71% of average.
  • However, because of above-average precipitation from September 2016 through June 2018, natural streamflow is near average throughout the watershed.
  • Winter flow out of Island Park Dam has averaged 516 cfs since December 1, compared with the 1978-2018 average of 351 cfs.


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