Ecological risks assessment of organophosphorus pesticides on bloom of Microcystis wesenbergii

► Hormesis induced by four tested organophosphorus pesticides on Microcystis wesenbergii was observed. ► Parameters of chlorophyll fluorescence was significantly stimulated and varied with OPPs species and concentrations. ► Taken OPPs as sole phosphorus source, no observable hormetic effect was detected in chlorophyll fluorescence. ► Abusive utilization of OPPs might induce competitive advantage and formation of M. wesenbergii bloom.