Analysis of the frequency of occurrence showed that in both reservoirs studied, most species were rare and occasional (Figure 3, Table 2). There were no very frequent species in the Itaparica reservoir. However, in the frequent category, the following species were observed: the cyanobacteria Cylindrospermopsis raciborskii (Woloszynska) Seenaya & Subba Raju, the diatoms Aulacoseira ambigua (Grunow) Simonsen and A. granulata (Ehrenberg) Simonsen and the green algae Pediastrum duplex Meyen and Planktosphaeria gelatinosa G.M. Smith (Table 2).