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The release of anthropogenic chemicals to streams, stemming from contaminated sites, direct application (rural/urban) or accidental release, represents a significant threat to water resources and thus the health of humans and aquatic ecosystems. Predicting the transport and fate of chemicals is key to quantify contaminant concentrations and develop environmental quality standards (EQS). Tracer tests are a well-established tool for such hydrological investigations in various water-based systems. In stream settings, such experiments have predominantly investigated longitudinal mixing and flow velocities by measuring the tracer concentration in a few discrete locations; few studies have focused on the transversal mixing properties. Recent progress in hyperspectral remote sensing from unmanned aerial systems (UAS) allows advancing the two-dimensional monitoring of tracer tests, by mapping the tracer concentration with a high spatial resolution in narrow streams with difficult accessibility. So far, such methods have only been demonstrated in controlled settings or in ocean waters, but not in optically complex streams. In this study, we evaluated the performance of a miniaturized hyperspectral imaging system and a consumer grade camera on board of an UAS, to map the concentration of the fluorescent tracer Rhodamine WT in a stream impacted by a contaminated site. In order to estimate tracer concentrations from the remotely sensed data, a band ratio of the red and blue band was used for the photo camera, while a vector based method, estimating the spectral angle in regards to a reference spectrum was applied for the hyperspectral data …