The non-toxic dye rhodamine WT can be added to streams and lakes to trace water movements. Here, the dye is being released to measure how water in Spring Creek flows into Bull Trout Lake, and the distribution and residence time of the water in the lake.
The study was part of a larger analysis of nitrogen movement through watersheds. The student in the photo is preparing an additional tracer drip of bromide (another water mass tracer) and 15N-nitrate as part of a research program to measure nitrogen movement through watersheds. The NSF-funded study was conducted by researchers at Utah State University and Montana State University.