Photo of “algae bloom” in the mainstem Gallatin River by Rich Addicks.

The Task Force and the Montana Department of Environmental Quality (MT DEQ) first identified an “algae problem” in the West Fork Watershed in 2005 by monitoring both nutrients and algae biomass. Algae biomass data from 2005 and 2008 suggested that algae growth exceeded state standards in the West Fork and South Fork of the West Fork and was elevated in the Middle Fork of the West Fork.

In 2010, the West Fork Watershed TMDL study designated the West Fork, Middle Fork, and South Fork to be impaired or exceeding state standards for nutrients. This designation took into account algae biomass data.

The Task Force and citizens have documented a “green trail” from the West Fork confluence to the Big Sky Golden Gate bridge (about 3 miles downstream of the intersection of HWYs 191 and 64) for several years. The Task Force has documented algae growth at 21 monitoring sites with photos since 2014.

The Task Force received multiple reports of unprecedented algae growth on the mainstem Gallatin River in 2018. We are in the process of collecting algae biomass data for 21 sites on the Gallatin River, Taylor Fork, West Fork, Middle Fork, South Fork, and North Fork.