An aluminum reduction plant began operation in Flathead County, Montana, near Columbia Falls in 1955. A consequence of the electrolytic reduction process used in the plant is the generation of gaseous and particulate fluoride air pollutants. In 1957 foliage injury symptomatic of excessive accumulation of fluoride was identified in the vicinity of the plant. Following plant expansions, visible injury to flora was detected in the southwestern part of Glacier National Park, which at its nearest point is about 6 miles northeast of the aluminum plant. The report discusses meteorological and air quality investigations conducted by the Environmental Protection Agency, along with extensive investigations of fluoride accumulation in indigenous vegetation in the area.