To support research on dispersion in river channels, a tracer dye experiment was performed on the Kootenai River in northern Idaho, September 25-27, 2017. This data release provides in situ field measurements of Rhodamine WT dye concentration acquired during the experiment. A pulse consisting of 72.57 kg (160 pounds) of KEYACID™ Rhodamine WT dye that was 20% Rhodamine by weight was introduced into the Kootenai River channel from a single release point at the Kootenai Tribal Fish Hatchery over a period of 90 seconds ending at 20:10:40 PDT on 9/26/2017, which is equivalent to 04:10:40 on 9/27/2017 UTC. Information on the timing and location of the dye release is available from the KootenaiDyeReleasePoints.kmz Google Earth placemark file included in this data release. Following the release, measurements of dye concentration in units of micrograms/liter were made with a set of five water quality sondes (Turner Designs C3 submersible fluorometers). Four of these sondes were deployed in a stationary, moored configuration to record time series at a single fixed location. A fifth sonde was deployed from a jet boat and used to record a longitudinal profile down the channel as well as a series of cross-sections to quantify lateral variations in concentration. All of these measurements are geo-referenced (UTM Zone 11N, NAD83) and provide information on spatial and temporal variations in dye concentration as the Rhodamine plume dispersed along and across the Kootenai River following the initial release. The measurements continued for nearly 40 hours after the release and the discharge during this time period remained steady, with a mean of 198.4 m3/s and standard deviation of 7.1 m3/s as measured at the USGS gaging station at the Tribal Hatchery (#12310100). The data are provided in text files (.csv) and shapefiles that include spatial information (coordinates of each measurement) and UTC time stamps as well as the measured concentrations in micrograms/liter. These field measurements of Rhodamine dye concentration, along with related remotely sensed data sets included in associated data releases, were used to assess the potential for estimating tracer dye concentrations from remotely sensed data to support studies of dispersion in river channels. In addition, the concentration data were used to support and validate hydrodynamic numerical models of flow, dispersion, and Lagrangian particle tracking.