HFF Blog

Fish of the Month: Year Two

Photo of Rainbow Trout.

Last year at this time, I reported on year one of my resurrection of “fish of the month,” a tradition that Henry’s Fork Anglers guide Tom Grimes and I started many years ago. The goal is to catch at least one wild trout every month of the year, on a fly, in our local Idaho, Montana, and Wyoming waters. My longest fish-of-the-month streak lasted 55 months, from July 2004 through January 2009. On Thursday December 15, 2016, I successfully added month 24 to the current streak.

Island Park Reservoir update 12/18/2016

Photo pf rainbow trout

Conditions at Island Park Reservoir as of 12/17/2016

  • Reservoir contents: 72,446 acre-feet (53.6% of capacity)
  • Mean outflow since 12/10/2016: 164 cfs by USGS gage; 161 cfs by USBR gate setting
  • Mean streamflow through Box Canyon since 12/10/2016: 354 cfs
  • Inflow: 0 cfs from Henrys Lake + 360 cfs reach gain from Henrys Lake to IP
  • Mean storage rate since 12/10/2016: 386 ac-ft per day
  • Total storage since 9/13: 51,965 ac-ft (starting value was 20,481 ac-ft)

Water Supply Overview

Turbidity persistence test: conclusions from the 2016 data

This fall HFF initiated a new water-quality monitoring study designed to answer the following question: How far downstream of Island Park Dam (IP Dam) do high turbidity levels persist? I introduced this study in my blog post made on September 9, 2016. Please find details of the background and motivation for this study, as well as a map of the sampling sites, in the previous blog post. The current blog post summarizes what we found during our 2016 data collection season.

Island Park Reservoir update 11/10/2016

Photo of rainbow trout.

Conditions at Island Park Reservoir as of 11/10/2016

  • Reservoir contents: 54,480 acre-feet (40.3% of capacity)
  • Outflow: 100 cfs, according to recently adjusting USGS rating
  • Estimated streamflow downstream of the Buffalo River: 290 cfs
  • Inflow: 0 cfs from Henrys Lake + 375 cfs reach gain from Henrys Lake to IP
  • Mean storage rate since Henry’s Lake Dam outflow was reduced: 518 ac-ft per day
  • Total storage since 9/13: 33,999 ac-ft (starting value was 20,481 ac-ft)

Overview

Wet weather continues

Photo of Fall River.

Conditions at Island Park Reservoir as of Friday morning, 10/28/2016

  • Reservoir contents: 45,142 acre-feet (33.4% of capacity)
  • Outflow: 110 cfs by USBR gates; 75 cfs by USGS gage
  • Estimated streamflow downstream of the Buffalo River: 300 cfs
  • Inflow: 60 cfs from Henrys Lake + 430 cfs reach gain from Henrys Lake to IP
  • Mean storage rate since my last report on 10/16: 687 ac-ft per day
  • Total storage since 9/13: 24,661 ac-ft (starting value was 20,481 ac-ft)

What do macroinvertebrates tell us about the Henry’s Fork?

Photo of salmonfly nymph.

Highlights

  1. Aquatic macroinvertebrates—insects and other creatures that live in the stream bottom—feed trout and are the basis of fly-fishing on the Henry’s Fork, but they are also important indicators of aquatic habitat quality.
  2. HFF is two years into a long-term program of monitoring aquatic macroinvertebrates at Flatrock, Last Chance, Osborne Bridge, Ashton, and St. Anthony.
  3. Primary conclusions from comparison of 2015 and 2016 data are:
    1. Abundance of macroinvertebrates averages about 47,000 individuals per square meter of stream bottom across all sites.
    2. Mayflies, stoneflies and caddisflies dominate the invertebrate assemblage at Flatrock, Last Chance, and Ashton, but are outnumbered by other organisms at Osborne and St. Anthony.
    3. Aquatic habitat quality ranges from excellent at Flatrock to good at St. Anthony, decreasing with distance downstream from the headwaters.
    4. The only statistically significant differences between 2015 and 2016 occurred at Osborne Bridge, where total abundance of invertebrates decreased—primarily because of a decrease in non-insects—and where habitat-quality index increased, reflecting an increase in percentage of mayflies, stoneflies, and caddisflies.
    5. Most of the mayflies and stoneflies important to fly anglers were found at all five sites. These were pale morning dun, flav, blue-winged olive, green drake, trico, brown drake, and yellow sally.

Precipitation Continues to Headline HF Water Situation

Henrys Fork near Marysville, with snow-covered Teton Range in background

Conditions at Island Park Reservoir as of midnight, Monday 10/17/2016

  • Reservoir contents: 37,588 acre-feet (27.8% of capacity)
  • Outflow: 129 cfs by USBR gates; 71 cfs by USGS gage (see below)
  • Inflow: 60 cfs from Henrys Lake + 560 cfs reach gain from Henrys Lake to IP
  • Mean storage rate since last flow adjustment, made October 6: 699 ac-ft per day
  • Total volume of water stored since storage began on September 13: 17,108 ac-ft

Overview

Island Park Reservoir Continues to Fill Rapidly

Early October snow at Island Park Dam

Conditions as of 12:00 a.m. Oct. 11, 2016

  • Reservoir contents: 33,384 acre-feet (24.7% of capacity)
  • Outflow: 127 cfs by USBR gates; 76 cfs by USGS gage (see below)
  • Inflow: 60 cfs from Henrys Lake + 425 cfs reach gain from Henrys Lake to IP
  • Mean storage rate since last flow adjustment, made October 6: 695 ac-ft per day
  • Total volume of water stored since storage began on September 13: 12,904 ac-ft

Overview

Projected Winter Flow Below Island Park Dam

Rainbow over Henry's Fork River.

Island Park Reservoir update, 10/3/2016

In this blog, I provide:

  1. an update on current conditions at Island Park Reservoir (20% full, filling at 400 ac-ft per day, with 7,500 ac-ft filled already this fall),
  2. a review of management objectives (lower flows to 60-70 cfs by mid-October, while keeping flow at St. Anthony around 850 cfs),
  3. my best estimate of fall and winter operations and winter flows at the dam (120 cfs from the dam + 180 cfs from the Buffalo River after November 20),
  4. analysis of USGS streamflow measurement at Island Park (consistently lower than outflow measured through dam gates as plants have decayed), and
  5. some statistics on how water year 2016 stacked up (only slightly better than 2015 and second lowest natural streamflow since 1979).

Brown Trout Redds

The aspens are yellow, the mornings are frosty, and the Brown trout (Salmo trutta) are staging to spawn. Brown trout, like many of their salmonid cousins, migrate from lakes, oceans, or main-stem river reaches to headwater habitat to dig redds (nests in the gravel) and deposit their eggs­1. For Brown trout in the Upper Snake River region, many don’t have access to headwater habitat due to hydraulic barriers and will spawn in main-stem river reaches instead.

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