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Construction of central Poland's Jeziorsko Reservoir in 1986 has been followed by a 30-year period of secondary succession in the direction of zonation of vegetation typical for the valley of a major river. While the southern part is protected as an ornithological reserve, the whole area falls within the Jeziorsko Reservoir Natura 2000 area called „Jeziorsko Reservoir", there have never been more intensive geobotanical studies carried out here - hence. The aim of our work to describe the plant cover in the area of the river Warta's inflow and discharge into the Reservoir. To the above end, field studies were conducted along 6 transects (10 m wide and 513 to 2416 m long, depending on the influence of surface waters) intended to reveal abrasive, accumulative and stabilised impacts of water. Thus, while erosion and long-term inundation prevail in the north, the middle part features a river of braided form, with many arms and old river beds, with a prevalent process of the accumulation of river sediments. In turn, in its southern studied part, the river channel has been straightened, and the wider valley is cultivated. The flora here is not rich (with just 235 taxa of vascular plant), and this is deemed to reflect habitat uniformity and limited anthropopressure. The spectra of life forms and of geographical/historical groups of species along the transects do nevertheless present distinct differences. Native species dominate (to the tune of 91.4-96.1%), but the northern part under lesser human impact mainly has non-synanthropic spontaneophytes, while the southern area with its meadows and pastures supports apophytes. Anthropophytes do not extend over any more-major area, and pose not competition to native flora, contemporarily at least. The group of endangered species is only represented by Najas marina and Pulicaria vulgaris; both in the NT category. Najas marina is also present on the IUCN Red List, with the same status. Though rare in Poland in general, Ulva flexuosa was found to occur quite frequently in the Reservoir. Regionally endangered status would in turn apply to both Populus nigra (LC) and Senecio paludosus (VU). The similarity of actual vegetation to potential natural vegetation can be explained in terms of regular inundation and limited human influence. Factors hindering the process of spontaneous succession entail active bird-protection measures that involve the removal of trees and shrubs (over 70 ha in 2016). Away from the Reservoir itself - with its differentiated hydrophytic vegetation - the association accounting for the highest share of plant cover, and also present in the delta of the Warta and along old river beds, is Salicetum albae. Permanent herbaceous vegetation is represented by different swamp communities. On river banks and within the complex of forest or swamp, willow scrub of the Salicetum triandro-viminalis type has emerged. In turn, temporarily-exposed bottom areas support therophytic communities. The meadows prevalent in the vicinity of Warta town are mostly the subject of regular mowing. Grazed swards were also found within forests, their presence evidently being promoted by the activity of wild animals. Ruderal vegetation was scarce, like the psammophilous grassland vegetation found only on embankments. The total number of plant communities observed was 80, and the highest shares (68% to over 92%) were of natural communities. The endangered communities categorised as facing an unidentified threat (I) were 26 in number, while the E (endangered) category was ascribed to Populetum albae only. 8 protected Natura 2000 habitats were identified, as represented by 20 communities. Among these are psammophilous grasslands and slightly halophilous pastures not typical of this area, and hence very limited. All others communities proved to be very well-developed and common. The vegetation map presents the distribution of 6 vegetation formations (forest, scrub, riverside therophytes, reedswamp, grazed pasture and meadow and hydrophytic vegetation). The central part of the studied area, in which all of these formations create a mosaic, is most differentiated. This fact was confirmed by the highest recorded value for the Shannon-Wiener diversity index. The diversity of vegetation and dynamics of succession processes related to the activity of surface waters indicate a need for legal protection, not only of birds, but also of habitats. This area well exemplifies phenomena linked with the activity of a large river, with a diversity of vegetation in successional series of a kind that it is no longer possible to find below the Reservoir dam. [ABSTRACT FROM AUTHOR]