These data files include 2 years (2018-2020) of high-frequency in-situ chlorophyll-a and phycocyanin fluorescence sensor (Turner Designs, Cyclops 7F) data, together with data from various tests conducted with these sensors. Morever, in-vitro chlorophyll-a data for 2018-2020 period is also included. These data are collected in Lemming mesocosm site, Denmark, where there are 24 tanks with 2 nutrient and 3 temperature treatments (2x3 factorial design). There is data from 24 in-situ chlorophyll-a and 12 in-situ phycocyanin fluorescence sensors. In this Dataset folder, there are: one Metadata (*.xlsx) file with 3 sheets; "Descriptive": comprises information on location, authors, study period and the main instrument used, "Structural": includes detailed information on each dataset. "Relational": includes a figure showing the relations between the datasets thirteen files (*.csv) in LemCP_DataORE that were used to; conduct in-situ fluorescence sensor tests (i.e. blank variation, linearity check, DOC effect check), calibrate 24 in-situ fluorescence chlorophyll-a sensors plot various figures