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Scientific Study Releases Harmless Yellow-Green Dye into Fernan Lake

July 30, 2018

A yellow-green dye that will temporarily discolor the east end of Fernan Lake starting Thursday, Aug. 2, is harmless and part of a scientific study.

Professor Frank Wilhelm with the Department of Fish and Wildlife Sciences at the University of Idaho and his research team will inject the bright yellow-green fluorescent dye into the east end of Fernan Lake on two occasions between Thursday, Aug. 2 and Friday Aug. 9, in an area adjacent to the lake’s east end lily pads.

The dye will be used to obtain information on the distribution, direction of movement and travel time of nutrients that enter the lake from a wetland on the east side of the lake and how that dispersion relates to wind-induced water currents on the lake. Results of the study will be provided to various state agencies to help with tracking of nutrients in Fernan Lake.

The dye, which has been used in hydrologic studies for decades, is approved as a tracer in drinking water and is safe for aquatic life in the concentrations used in this study. Concentrations of the dye after release will be measured using a combination of fixed monitoring sites and an unmanned aerial vehicle. Two releases are planned to track water movement in response to up-valley and down-valley winds.

“By using low, non-hazardous concentrations of dye, we can identify circulation patterns and water exchange between the lake and wetland to quantify the nutrients entering the lake,” said Wilhelm, a limnologist in U o f I’s College of Natural Resources. “Understanding the pathways and behavior of lake inputs will allow better management of lake resources.”

Weather permitting, the first injection of dye solution will occur early Aug. 2, with a second release planned Aug. 9. Measurements will be made near the injection point and outward into the lake for distances of up to one-third of a mile. The dye is expected to break down naturally in between three to five days and will not attach to particles in the water or affect aquatic life.

Anglers are advised to process their catches as usual by rinsing in clean water. Although the dye is harmless to swimmers, due to an ongoing blue green algae bloom in the lake, swimmers are advised to consult the recent health advisory issued by the Panhandle Health District on July 18, 2018.


Media Contact:

Frank Wilhelm

U of I Department of Fish and Wildlife Sciences



About the University of Idaho

The University of Idaho, home of the Vandals, is Idaho’s land-grant, national research university. From its residential campus in Moscow, U of I serves the state of Idaho through educational centers in Boise, Coeur d’Alene and Idaho Falls, nine research and Extension centers, plus Extension offices in 42 counties. Home to nearly 12,000 students statewide, U of I is a leader in student-centered learning and excels at interdisciplinary research, service to businesses and communities, and in advancing diversity, citizenship and global outreach. U of I competes in the Big Sky Conference. Learn more at