South Fork Lower Willow Creek Fish Passage Project

By Tess Scanlon

Project Summary:

In October 2021, TU and partners completed a priority fish passage project on South Fork Lower Willow Creek to reconnect 14 miles of westslope cutthroat trout habitat and eliminate entrainment of fish into an irrigation ditch. South Fork Lower Willow Creek is a priority stream for native fish conservation that supports high densities of native fish species, including a genetic isolate population of westslope cutthroat trout that is protected from introgression with rainbow trout by the downstream Lower Willow Creek Reservoir. The pure cutthroat population in South Fork Lower Willow Creek is especially important, because it is used by Montana FWP as a source population for the Washoe Hatchery, Montana's only native cutthroat fish hatchery located in Anaconda, MT. 

Description of Project Work: 

With support from the WestSlope Chapter and other project partners, TU replaced the existing irrigation diversion structure and installed a fish screen on the associated irrigation ditch. The diversion blocked fish passage in the summer and the ditch was entraining thousands of juvenile cutthroat and other native fish from April through Octobert. A new rock weir diversion structure was build to improve the control of water into the ditch. The diversion functions like a natural rock-step feature in the stream and allows year-round fish passage of all age class fish, plus it reduces erosion and protects riparian habitat at the diversion site. In addition, a "Farmers Conservation Alliance" or FCA screen was installed in the ditch to eliminate entrainment of fish into it.  

WESTSLOPE CHAPTER SUPPORT: $5,000 

Total Project Cost: $70,000 

Funds Leveraged (see total match below): $ 65,000

Photo 1. BEFORE –Looking downstream at the tarp and pole fish passage barrier irrigation diversion dam structure in South Fork Lower Willow Creek. Photo Taken summer 2020. 

Photo 2. AFTER – looking downstream at the newly installed rock weir irrigation diversion replacement structure installed to reconnect fish passage in South Fork Lower Willow Creek. Photo taken October 2021. 

Photo 3. BEFORE – looking upstream at the tarp and pole fish passage barrier irrigation diversion dam structure in South Fork Lower Willow Creek. Photo Taken summer 2020. 

Photo 4. AFTER – looking upstream at the newly installed rock weir irrigation diversion replacement structure installed to reconnect fish passage in South Fork Lower Willow Creek. Photo taken October 2021. 

Photo 5. During construction, looking down ditch at fish screen installation in South Fork Lower Willow Creek irrigation ditch. Photo taken October 2021. 

Photo 6. AFTER – looking down ditch at the newly installed fish screen on South Fork Lower Willow Creek irrigation ditch. Photo taken October 2021.