A permanently moored thermistor chain at the deepest point in Lough Feeagh measures water temperature at 13 depths (0.9, 2.5, 5, 8, 11, 14, 16, 18, 20, 22, 27, 32, 42). This dataset comprises data collected between 2004 and 2019 which has gone through detailed QA"QC. More recent data can be requested or downloaded from the Marine Institute through www.marine.ie. The dataset also includes the bathymetry of Lough Feeagh. The thermistor chain data are provided as a text file. Users of the R statistical programming language may open this through the rLakeAnlyzer package https:""cran.r-project.org"web"packages"rLakeAnalyzer"rLakeAnalyzer.pdf The dataset was originally published with a doi in October 2018 and was updated in May 2020 to include 2018 and 2019 water profiles. This DOI has been superseded by https:""doi.org"10.20393"91ff84cc-a10d-45d0-9b30-e2d11a040e95 due to corrections applied to the dataset. Long-term Ecological Monitoring