The aim of this work was to increase the taxonomic knowledge and the spatial and temporal distribution patterns of the genus Pinnularia in the Amazon region. The present study was carried out in Verde lake, a clear water flooding environment of the Tapajós river basin, located in the Alter do Chão Environmental Protection Area. The samples were collected monthly with plankton net (20 μm) at four sampling stations, from July 2016 to June 2017, totaling 48 samples, stored in 100 mL flasks and fixed with Transeau solution (Bicudo e Menezes, 2006). Concomitantly to the samples, measurements of pH, electrical conductivity, dissolved oxygen, temperature, water transparency and depth were performed. To carry out the analysis, aliquots of samples were submitted to the oxidation process for analysis by optical microscopy and scanning electron microscopy. Based on the observation of the permanent slides, the specific richness in the samples was recorded and the constancy index for each taxon was calculated. Principal Component Analysis (PCA) was applied to detect interrelations between environmental variables and sampling stations. To verify if there was a significant difference in the community of Pinnularia, between seasons and between the periods of the flood pulse, the PERMANOVA test was applied using the Jaccard similarity index. The Redundancy Analysis (RDA) was performed to verify the significant relationships of the environmental variables on the community of Pinnularia. The diatom community of the genus Pinnularia consisted of 60 taxa (30 species, 11 varieties, 9 conferatum and 10 taxa identified in the generic level), Six of which were cited for the first time for the Brazilian Amazon: Pinnularia acuminata var. novazealandica, P. divergens var. media, P. graciloides var. rumrichae, P. parallela var. parallela, P. percuneata var. percuneata, P. tumescens, and 21 cited for the first time in the state of Pará: P. amazonica, P. aquaenigrae, P. boyeriformis, P. confirma, P. divergens var. malayensis, P. divergens var. mesoleptiformis, P. hyalina, P. instabiliformis, P. instabilis, P. liyanlingae, P. manausensis, P. meridiana var. concava, P. mollenhaueri, P. pogoii, P. polyonca, P. rostratissima var. ventricosa, P. sterrenburgii, P. subboyeri, P. tupensis, P. viridiformis, P. viridis. The species richness was higher during the decreasing water period (57 taxa), followed by low water periods (52 taxa), increasing water (48 taxa) and high waters (40 taxa). Regarding the hydrological cycle, the results showed that there was a significant difference in the population of Pinnularia genus in the periods of decreasing water, low waters and high waters. Spatially, the station called IM - Igarapé do Macaco differed from the other collection stations. The RDA indicated that the environmental variables depth and pH influence the distribution of most species of the genus in the Verde lake, where the majority of the taxa were associated to the low water and decreasing water periods, in which there are more acidic environments and with lower depths.
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