The Upper Delaware River is a unique example of an aquatic system where summer river temperature is actively managed for ecological purposes. River temperature at the mainstem Delaware River at Lordville, NY gage (USGS 01427207) is targeted to remain below 25°C, with warm events potentially mitigated via directed upstream reservoir releases, a process guided by predictive tools. These directed releases currently occur at the Cannonsville Dam on the West Branch, though the temperature criteria at the Lordville gage is also influenced by releases from the Pepacton Dam on the east branch. To increase the spatial resolution of summer river temperature data available for understanding river temperature processes and informing predictions, 40 Onset Tidbit water temperature loggers (models MX2203 and v2 running at 15 min collection intervals) were attached to masonry bricks and deployed temporarily along the riverbed along the East Branch, West Branch, and mainstem Delaware River down to the Lordville gage. The common deployment period for these temperature loggers was 7/23/21 to 8/29/21, and due in part to several high flow events over that period, 26 loggers were ultimately recovered with data. There were three consecutive days (8/10 to 8/12/21) of thermal mitigation dam releases during the logger deployment period. While most of the recovered temperature loggers were relatively clean of sediments when found, four sites showed accumulation of alluvial fines over the loggers which may have impacted recorded river water temperatures, as listed in the read.me file on this root page. Potential deposition of sediments on the temperature loggers at other points over this record is unknown, though several turbid river flows did occur during the period. This public data release contains raw instrument export files (.csv format) and ‘processed’ temperature data. River temperature data in the ‘Combined_Temperature_Data.csv’ file have been trimmed to individual logger deployment times, the time zone may have been adjusted to UTC-05:00, and all records were resampled at a common 15-min interval; but have otherwise not been manipulated from the raw data. The Tidbit temperature loggers were all newly purchased when deployed and were assumed therefore to be calibrated and operating at the manufacturers reported specifications (accuracy +/- 0.2°C, resolution 0.01°C).