Diversion Dam Removal: Trout in Jefferson may have more access to spawning areas, thermal refuge

Trout in the Jefferson River may have more access to spawning areas and thermal refuge thanks to a new partnership recently announced by Montana Trout Unlimited (MTU) that will remove three aging diversion dams on the Boulder River. MTU is collaborating with Barrick Gold, owners of the Golden Sunlight Mine, with complimentary support from Montana Fish, Wildlife & Parks (FWP), Natural Resource Conservation Service (NRCS), and L.R. Huckaba Ranch on the Boulder River near Cardwell, MT to increase stream flow and connectivity on the Boulder.

"We commend Barrick and Golden Sunlight for taking a proactive approach to replace deteriorating infrastructure and for considering the potential benefits for the river and all the creatures that rely on it," said Chris Edgington, MTU's Jefferson Watershed Project Manager. "With trout numbers near, or at historic lows across much of Southwest Montana, there's no better time for a water quantity and quality project in this area. This is a great example of the win-win projects Montana Trout Unlimited strives to develop."

Rising in the mountains north of Butte, the Boulder River is the largest tributary to the Jefferson River downstream of the Beaverhead-Big Hole River confluence, providing a boost of cold water near the midpoint of the Jefferson's 83-mile length. The Boulder is a high-value coldwater fishery and provides significant agricultural production in Jefferson County. On the Candlestick Ranch, the Shaw Diversion Dam and two smaller diversions deliver water to 233 acres of cropland. The aging infrastructure is getting more difficult to operate and regulate irrigation withdrawal. This project will alleviate infrastructure concerns, by removing the diversion dams and replacing them with instream irrigation pumps, thereby providing a significant ecological uplift to the Boulder and Jefferson Rivers through stream restoration, water savings, continued agricultural benefit, and wetland development.

"We are excited to partner with Montana Trout Unlimited in the removal of a diversion from the Boulder River. This collaborative effort will help to ensure a healthy and thriving fishery for future generations. Barrick's dedication to our community as well as the surrounding wildlife exemplifies our commitment to building sustainable legacies," said Kristine Murphy, Golden Sunlight General Manager.

"This project is a win-win for trout and property owners, and we couldn't be more excited to see it get off the ground," said Edgington.

In April 2021, the partners met to discuss the challenges at the project site, to share what resources they could provide, and what the potential outcomes of the project could be. MTU, along with FWP and NRCS, developed a plan to collect baseline data to quantify project benefits. Methods of data collection have included stream and irrigation flow monitoring, continuous temperature monitoring, fish population estimates, redd counts, juvenile trout out-migration surveys, and a wetland delineation.

Quantifiable project benefits include:

• Improving irrigation delivery and efficiency to 233 acres of valuable cropland

• Achieving 7 CFS of cold Boulder River water savings over the current base flow of 28 CFS

• Providing fish and other aquatic organism passage for thermal refugia and spawning

• Eliminating fish entrainment in 3 irrigation ditches

• Reducing nutrient and sediment loading

• Creating wetlands

"The project adds about 7 CFS of summer flow to the Jefferson River, and Boulder River water is 2 to 3 °F cooler than the Jefferson during August," said Ron Spoon, FWP Fisheries Biologist.

Planning, engineering, and design for the dam removal and stream restoration will begin this fall. The partners anticipate project implementation in the fall/winter of 2025. For more information on this project, contact Chris Edgington at [email protected].