Toxic cyanobacteria in public water supply reservoirs represent a serious health risk since they can release potent cyanotoxins into the water. Among the cyanotoxins are saxitoxin (SXT) and its homologs that form a group of potent neurotoxins called paralytic shellfish toxins. Few studies have focused on occurrence of saxitoxin and the genes involved in the biosynthesis in oligotrophic freshwaters.