fbpx Skip to content

South Fork of the Snake Flow Update and Macroinvertebrate Monitoring


Flow out of Palisades Reservoir remains at the typical winter flow of ~900 cfs.  This flow will be maintained through mid-March.  Of particular interest for 2019 is the fact that the Idaho Fish and Game and the Bureau of Reclamation are not going to be conducting the spring freshet.  It’s been determined that simulating a spring run-off event does not decrease the population of non-native rainbow trout so it’s been discontinued.

The population of rainbow trout continues to increase threatening the native cutthroat population and pressuring officials to manage differently to avoid the possibility of the Yellowstone Cutthroat Trout (YCT) being listed as an endangered species and bring the South Fork under federal control and regulations.  If you love the South Fork and YCT the best thing you can do is keep and eat the rainbows.

South Fork Initiative Starts Macroinvertebrate Monitoring

The South Fork Initiative (SFI) was officially announced in November of last year.  It’s a collaborative effort launched by the Henry’s Fork Foundation in partnership with local outfitters and concerned citizens.  You can learn more about it here.

SFI’s Mission Statement

To conserve, protect, and restore the unique fisheries, wildlife, and aesthetic qualities of the South Fork of the Snake River and its watershed for all individuals and for future generations. 

Macroinvertebrate Monitoring by Bryce Oldemeyer

In March 2019, the South Fork Initiative will begin long-term monitoring of aquatic macroinvertebrates on the South Fork of the Snake River (SFSR) Just like on the Henry’s Fork, the Henry’s Fork Foundation/SFI will use standardized sampling methods at various sites throughout the SFSR to understand the density, diversity, and distribution of aquatic macroinvertebrates in the SFSR.

macroinvertebrate sampling on Henry's Fork
Annual macroinvertebrate sampling on Henry’s Fork. Photo credit: James Chandler
Aquatic macroinvertebrates (insects and creatures that reside in the river bottom) are a critical component of a healthy ecosystem and fishery. Understanding the diversity and density of macroinvertebrates through time and space is critical for understanding habitat quality, hatches, and trout forage within a river. Additionally, using standardized sampling methods at the same sites over multiple years can help identify environmental mechanisms driving changes in species abundance and diversity through time. Collecting this data will be helpful for answering questions or comments such as, “It seems like the PMD hatch was terrible this year. I wonder if there were fewer bugs than previous years, or if high flows were just making it harder to fish during the hatch”, or “There is a ton of rock snot (aka periphyton) this fall. I wonder if this is going to affect the bugs?”
If you’d like an example of how we have used macroinvertebrate data on the Henry’s Fork, I highly encourage you to read Rob Van Kirk’s blog “What do macroinvertebrates tell us about the Henry’s Fork?