Differences in the phytoplankton community structure, abundance and environmental variables between upstream and downstream sites were maximal during lowflow periods. Chlorophytes and dinoflagellates were present during lowflow
periods upstream of the reservoirs and in the intermediate site.Cocconeiscf.placentulacharacterized the
downstream section, associated to the presence of macrophytes in that section. The present study sheds
light on the consequences of river regulation under potential scenarios of climate change, and results could
be used to anticipate ecological problems in large regulated rivers under these circumstances.