A reach of the Sacramento River near Glenn, California, was selected as a field site to test a sensor payload developed by the U.S. Geological Survey and the National Aeronautics and Space Administration for estimating surface flow velocities in rivers. The payload, called the River Observing System (RiOS), can be deployed from an uncrewed aircraft system (UAS). RiOS includes visible and thermal cameras, a laser range finder, an inertial navigation system, an embedded computer for storing and processing data, and a wireless link for transmitting data to a ground station. This data release includes thermal imagery acquired by RiOS and stored in Robot Operating System (ROS) *.bag files. The bag files are organized into two separate zip archives, one for each date of data collection. Foxglove Studio, an open-source data visualization tool, can be used to view the thermal images contained within the bag files (see link in Related External Sources). Once the thermal bag file is loaded in Foxglove Studio, open the settings and set the color mode to gradient and the minimum and maximum values to 12,000 and 15,000, respectively (see Foxglove.jpg in Attached files). The minimum and maximum values can be adjusted from these default values to enhance image contrast. The thermal images were used as input to an image velocimetry algorithm to estimate the surface flow velocities along the river. To assess the accuracy of these image-derived velocity estimates, field measurements of flow velocity were obtained using a SonTek M9 acoustic Doppler current profiler (ADCP) using the RiverSurveyor Live software package. ADCP measurements were collected along multiple pre-planned cross section lines oriented perpendicular to the primary downstream flow direction. At each transect, multiple ADCP passes were made and the data was then processed using the Velocity Mapping Toolbox (VMT) to produce mean cross sections (Parsons et al., 2013). The output from VMT consisted of a single comma delimited text file with the following seven column headers: 1) xs: the river transect stationing in meters; 2) x_meters: easting (x) spatial coordinate in meters; 3) y_meters: northing (y) spatial coordinate in meters; 4) depth_meters: depth in meters; 5) vmag_meters_per_second: the depth-averaged velocity magnitude in meters per second; 6) u_meters_per_second: east (u) component of the depth-averaged velocity vector in meters per second; and 7) v_meters_per_second: northing (v) component of the depth-averaged velocity vector in meters per second. The spatial coordinates are projected in Universal Transverse Mercator (UTM) Zone 10, World Geodetic System 1984 (WGS-84) datum.