In summer in Massachusetts, USA, preferential groundwater discharge zones are often colder than adjacent streambed areas that do not have substantial discharge. Therefore, discharge zones can efficiently be identified and mapped over space using heat as a tracer. This data release contains fiber-optic distributed temperature sensing (FO-DTS) data collected along the streambed interface of the main channel and tributaries of the upper Quashnet River, within approximately 1 km of Johns Pond, from June 14 to June 20, 2020. For these deployments a Salixa XT-DTS control unit (Salixa Ltd, Hertfordshire, UK) was used, and measurements were made over several day increments at 0.508 m linear resolution. Specific locations for collected data are located within the data files, and additional details are contained in the ‘readme’ files within each zipped data directory. Measured data in the form of Salixa instrument files are located in the 'Raw' data directory, including data collected along lengths of optical fiber that were not installed in the streams. The 'Processed' data directory contains data that have been aggregated from the original machine output files, spatially trimmed, and georeferenced. Additionally, simple summary streambed interface temperature statistics (mean, max, min, standard deviation) are listed by streambed location.