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Montana Watershed Coordination Council | P.O. Box 1416 Helena, MT 59624 | info@mtwatersheds.orgClick Here to Sign-up for our Watershed Newsletter

Reducing Risk in the Jefferson

The Jefferson Slough, a side channel of the Jefferson River.

This post was written by Big Sky Watershed Corps member Mark Werley as a part of a series reviewing the stops along the 2019 Missouri Headwaters Watershed Tour. Mark shares more about our stop at the Jefferson Slough and the work done there to combat aquatic invasive species.

Situated between the Tobacco Roots and the Highland Mountains, the Jefferson River is one of the three headwater rivers of the Missouri. Unlike its headwater siblings who are their own sources, the Jefferson River is primarily fed by its own major tributaries – the Big Hole, the Beaverhead, and the Ruby – and thus has important relationships with each of these rivers and their communities. The Jefferson River Watershed Council (JRWC) works closely with its headwaters partners to ensure the health of the Jefferson and the communities it supports.

This year, JRWC celebrated its 20th birthday, having been formed by irrigators and anglers who were concerned about water shortages and declining fish populations. From the start, the Council consisted of a variety of stakeholders: producers, recreationists, agencies, non-profits, and both municipal and rural communities. The watershed group was an early adopter of volunteer-based drought management planning, leaving them prepared when the drought of 2000 hit. 

JRWC has also been at the forefront of protecting the Jefferson from aquatic invasive species (AIS) – an initiative highlighted on the 2019 Missouri Headwaters Watershed Tour, attended by more than 70 watershed professionals from across Montana. Tour participants visited the Jefferson Slough, where, in 2011, a massive outbreak of the aquatic invasive plant Eurasian Water-Milfoil was discovered in this side channel of the Jefferson River. Eurasian Milfoil spreads through vegetative fragmentation; when one piece breaks off it will grow into a new plant, and the slough was dumping tens of thousands of pounds of the weed into the Jefferson River system.

Working with local landowners and other partners, including Jefferson County Weed District and Confluence Consulting, JRWC began to address AIS on the slough. Removal strategies included hand pulling of the weed and herbicide applications. The reduction of milfoil was evident, but connected tributaries such as Pipestone Creek continued to deliver high sediment loads in a low-power environment of the slough, providing ample milfoil habitat and a risk that the weed could continue spreading.

Tour attendees examine the stream gauge installed on the Jefferson Slough.

Utilizing the weed as a catalyst, JRWC was able to leverage funds to alter the Jefferson Slough stream channel. By abandoning a section of the existing channel, burying the milfoil, and repositioning the stream into a narrower floodplain that was deeper and allowed faster flows, the flushing of fine sediment out of the system began. As a result, JRWC and their partners were able to create an area with unfavorable conditions for AIS growth. Additionally, this project location had a real-time stream gauge installed to actively monitor streamflow and temperature data. These flow trends will be utilized in the next design phases of the Slough to produce high velocity stream channels to decrease the presence and spreading of Eurasian Milfoil.


To find out more about the Jefferson River Watershed Council, including current and past projects, visit their website