The Task Force and the Montana Department of Environmental Quality (MT DEQ) focused on monitoring algae in the West Fork Watershed between 2005 and 2017. The West Fork Watershed Total Maximum Daily Load study unearthed excess algae growth in the three tributaries in the Big Sky area: the West Fork, Middle Fork of the West Fork, and South Fork of the West Fork.

Map of impaired streams in the West Fork Watershed.

Citizens and Task Force staff have documented a “green trail” of algae beginning downstream of where the West Fork enters the Gallatin River and continuing to the Big Sky Golden Gate bridge (about 3 miles downstream of the intersection of HWYs 191 and 64), as well as an algae bloom below Wapiti Creek on the Taylor Fork, for several years.

In 2018, the Task Force received multiple reports of unprecedented algae growth in the mainstem Gallatin River downstream of the West Fork to Moose Creek, and from tributaries that flow into the Gallatin, including the South Fork of the West Fork, the West Fork, and the Taylor Fork. We have also received reports of spotty algae growth on the mainstem Gallatin River as far downstream as Storm Castle.

The Task Force is in the process of collecting and analyzing algae biomass samples from 21 sites located on the Gallatin River, Taylor Fork, West Fork, Middle Fork, South Fork, and North Fork to further investigate algae in the watershed. These analyses will help quantify the extent of algae growth, determine whether or not it is a threat to river health, and point to the cause of excess growth.

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