Phytoplankton, microscopic algae essential to aquatic ecosystems, are sensitive bioindicators of environmental change. This study explores the spatial and temporal dynamics of phytoplankton in Lake Tisza during the extreme summer drought of 2022. Monthly sampling from June to September across 28 sites a total 98 samples out of 112 were collected , identifying 416 taxa, mostly at the species level. Significant spatial and seasonal differences were found, with the Abádszalók basin showing the lowest diversity due to human impact and Tiszavalk the highest, influenced by water regulation. Variation was most pronounced between July and September. Phytoplankton composition was shaped by drought, water management, and the isolation of Tiszafüred, reflecting complex ecological responses. These findings support improved, location-specific strategies for ecological monitoring and drought-resilient water management.