This investigation was conducted to evaluate diagenetic elemental fluxes and different freshwater sources, including submarine groundwater discharge, in the water column of Puck Bay (Poland), southern Baltic Sea. Surface water samples were taken in June 2021. Water was pumped through a filter cartridge (1 µM pore size) into barrels and then through manganese-coated acrylic fibers to extract radium (Ra) isotopes. The Ra isotopes (224Ra, 223Ra) were measured within 3 and 10 days using radium delayed coincidence counters (RaDeCC). Subsamples were taken via PE syringes and filtered (0.45 µM, cellulose disposable acetate filters) for analysis of dissolved concentrations of major and trace elements and selected nutrients using ICP-OES (iCAP, 7400, Duo Thermo Fischer Scientific), dissolved ammonium (NH4+) by QuAAtro Analyzer System, dissolved inorganic carbon (DIC) and δ13CDIC using isotope gas mass spectrometry (MAT 253 coupled to a Gas bench II), and δ18OH2O, δ2HH2O using a CRDS system (laser cavity-ring-down-spectroscopy, PICARRO L2140- I).