Abstract <p>Based on the spores and pollen analysis of bottom sediments from the Varcha Bay (Krasnoyarsk Reservoir, Republic of Khakassia), changes in terrestrial vegetation in its basin since the reservoir formation and in the adjacent area following the construction of the Krasnoyarsk Hydroelectric Power Station have been found out for the first time. Two vegetation development stages have been identified. During the first phase (before flooding in 1967), when the bay was a small, endorheic Lake Varcha, not connected to the Yenisei River, wormwood steppes were widespread in its basin. The forest vegetation consisted of sparse pine clumps with few fir, spruce, and larch trees. During the second phase (1971–2024), after formation of the permanently deep Varcha Bay, the cognominal lake was replaced by sedge–grass meadows developed near the shores. Birch forests expanded, and willow, dwarf birch, and dwarf alder appeared. The results demonstrate changes in the terrestrial ecosystems in the south of Yenisei Siberia caused by the construction of a large water reservoir in the steppe zone.</p>