Vegetation in the river Danube was studied in 1972–2001 to document the changes associated with the construction of a water reservoir. Before 1993, only a single species of aquatic plant, Potamogeton pectinatus, was known to occur in the main channel of the river Danube, which forms the frontier between Slovakia and Hungary. In the 1980s the building of the Gabčíkovo hydroelectric power station started and was finished in 1993. At present, five different aquatic habitats occur in the study area. (i) In the upper part of the Čunovo reservoir, there are stands of reed; Zannichellia palustris and Elodea nuttallii were the first other macrophytes to colonize this area where there are now 11 species. (ii) The Old Danube consists of shallows and margins of the original riverbed, which since 1992 (1851–1811 river km) were occupied predominantly by Zannichellia palustris. The adjacent pools were colonized by Elodea nuttallii, Potamogeton species, Batrachium trichophyllum, Ceratophyllum demersum and Lemnaceae species, and Phalaris arundinacea dominates the littoral areas. (ii) The bypass canal harbours only the moss Cinclidotus riparius growing on the boulders. (iv) Two seepage canals were rapidly overgrown by macrophytes, many species of which were threatened species in Slovakia (Apium repens, Groenlandia densa, Hippuris vulgaris, Chara species). (v) Succession occurred in river arms on the left bank after the damming of the river which resulted in changes in spatial distribution and species composition of macrophytes; a North- American alien species Elodea nuttallii spread rapidly there.
Vegetation with species of Utricularia and that dominated by Eleocharis quinqueflora, which occupy the same habitats. was studied in minerotrophic mires and oligotrophic wetlands associated with ponds. Relative towater and soil chemistry, the communities of Utricularia ochroleuca s.l. and U. intermedia occurred in mineral-poor and those of U. minor and U. australis in mineral-rich conditions. Rare stands with U. vulgaris occurred in conditions that were intermediate in mineral richness. Four communities belonging to the class Isoëto-Littorelletea were distinguished. Vegetation without bladderworts and dominated by E. quinqueflora occurs in calcareous fens and belongs to the class Scheuchzerio-Caricetea fuscae (the Caricion davallianae alliance). Vegetation with U. intermedia is characterized by high vascular plant cover and belongs to the class Scheuchzerio-Caricetea fuscae. Utricularia ochroleuca s.l. prefers open, acidic and waterlogged depressions in peat, whereas U. intermedia grows mostly in the shade under vegetation canopy. In this study, U. minor and U. australis have been found mainly in the more alkaline and mineral-rich habitats, and both species also tolerated extremely high mineral richness.