Jefferson Slough Eurasian Watermilfoil Plan

for Jefferson County

Our monitoring efforts from 2016 to 2018 have indicated success in eliminating Eurasian Watermilfoil.

The problem

In 2011, a 20-acre infestation of Eurasian watermilfoil (Myriophyllum spicatum; EWM), was identified within a 4-mile segment of Jefferson Slough near Whitehall, MT.  This aquatic invasive plant is known to impede boat traffic, clog irrigation ditches and pump intakes, displace native aquatic plants, and reduce the abundance and diversity of macroinvertebrates, fish, mammals, and birds within infested areas.

our solution

To combat the infestation, we worked with a technical advisory committee in the development and implementation of a detailed management plan. This plan included:

  • Applying aquatic herbicide to the infested segment of the Slough
  • Relocating the Slough through a newly constructed and narrower adjacent channel
  • Modifying irrigation infrastructure along the Slough to enable periodic flushing flows and reduce the accumulation of fine sediments
  • Installing a sediment trap on Sheep Rock Creek to eliminate large sediment pulses during intermittent flows