Among the bloom-forming cyanobacteria, Microcystis aeruginosa is one of the most harmful species. The prevalence of toxic species and their toxicity profiles vary each year depending on environmental variables, despite their dynamics being not well understood. Imbalances in nutrient concentrations, the greater frequency and intensity of higher average temperatures and less severe winters, and the alternation between periods of positive and negative precipitation anomalies were identified as conditions favoring the prevalence of M. aeruginosa. Similarly, dry periods (corresponding to a prevailing La Niña condition) were even more conducive to the formation of harmful algal blooms of pronounced intensity. Moreover, toxin production is temperature-dependent and some strains are capable of producing multiple microsystins (MCs). Thus, the role of environmental variables in controlling the genetic expression of toxin synthetase of individual toxin-producing genes is still unknown.Facultad de Ciencias Exactas