This study presents and compares the floristic diatom composition of plankton and surface sediments of the water supply reservoirs from the Alto Cotia System (Pedro Beicht and Cachoeira da Graça reservoirs), located in the Reserva Florestal do Morro Grande. Samplings were carried out in seven sites, during the dry and rainy seasons and in the sediment surface during the dry season. Physical and chemical water parameters were analyzed. Twenty-three taxa belonging to 11 genera were identified. Morphometric data, relevant comments, and spatial location of the species were provided. Richness was higher in sediments, with eight exclusive species. The cluster analysis indicates that diatom species composition varied more between the compartments (water and sediments) than between the reservoirs or seasons. Present work adds three new citations to Brazil, besides four other species to São Paulo State, contributing to pioneer information in reservoirs considered as a reference in water quality for the metropolitan region of São Paulo.
algae; Alto Cotia Water Supply System; Bacillariophyta; flora; Reseva Florestal do Morro Grande
