SUMMARY1. Lake Kinneret is a warm (13–30°C) monomictic lake. Between January and June a heavy annual bloom of the dinoflagellatePeridinium gatunensedominates phytoplankton biomass (250 g m−2). At the beginning of the summer, degradation and decomposition of thePeridiniumbiomass occurs, serving as a trigger for intense sulphate reduction in the hypolimnion and sediments.2. The rates of sulphate reduction in the sediments varied seasonally from 12 to 1700 nmol SO4.−2reduced cm−3day−1in December and July, respectively. The availability of organic matter and sulphate is high in June after the crash of thePeridiniumbloom and the beginning of stratification and is lowest in December before overturn.3. Sulphate concentrations in the hypolimnion range between 0.52 mM and 0.20 mM during mixing (January‐April) and before overturn (December), respectively. The depletion in sulphate in the hypolimnion is stoichiometrically correlated to the increase in sulphide. The lake is not depleted of sulphate at any time, so the sulphate reduction process in Lake Kinneret is not limited by sulphate concentrations except in the sediments just bef