This data release includes geospatial datasets, comma separated values (.csv) files, and associated FGDC-compliant metadata representing data collected between 2004 and 2015 as part of a study of groundwater/surface-water interaction in the area of a lake-bottom permeable reactive barrier at Ashumet Pond, Falmouth, Massachusetts. The data sets are organized by type: (1) Fiber-Optic Distributed Temperature Sensing (FO-DTS) measurements of lake-bottom groundwater temperatures collected May 30-31, 2007, (2) Seepage meter data collected between November 2004 and August 2015, (2) Vertical temperature profile data collected between August 21, 2015 and September 3, 2015, and (4) Lakebed temperature measurements collected during three surveys in July 2008, August 2014, and August 2015. This data release is provided in support of the journal article: McCobb, T.D., Briggs, M.A., LeBlanc, D.R., Day-Lewis, F.D., and Johnson C.D., 2018, Evaluating long-term patterns of decreasing groundwater discharge through a lake-bottom permeable reactive barrier: Journal of Environmental Management, v. 220, p. 233–245, https://doi.org/10.1016/j.jenvman.2018.02.083. ; This data release contains all files required to replicate the results of the associated journal article.