The ecological state of the Kiev Reservoir affected by intensive contamination as a result of the accident at the Chernobyl Nuclear Power Station in 1986 was assessed in terms of the species-indicators of epiphytic algae occurring in the fouling of higher aquatic plants. It has been found that inhabitants of slowly flowing and moderately warm waters, alkaliphiles, indifferent organisms in relation to water salinity, nitrogen-autotrophic taxa tolerating elevated concentrations of organically bound nitrogen, β-mesosaprobionts and eurysaprobes (in relation to organic contamination) and eutraphentic organisms (indicators of the trophic state) prevailed in phytoepiphyton of the Kiev Reservoir. As a result of comparison of the original results with literature data obtained prior to the accident, it has been found that over a span of about 30 years (from the 1970s–1980s to 2010–2013), the taxonomic structure of phytoepiphyton remained almost unchanged. At the same time, the intensity of eutrophication, alkalization, and thermofication processes increased.