For algae, the Kaniv Nature Reserve is one of the most investigated sites in Ukraine. Soil algae have been thoroughly studied there (Boiko et al., 1984; Masiuk & Kostykov, 1984; Kostykov, 1985 a; Kostykov, 1985b; Kostykov, 1989; Kostykov, 1990; Kostykov, 1991; Kostykov & Rybchynskyi, 1995), whereas most information about aquatic algae, obtained before the Kaniv hydro-electric power station was built, is out of date (Oxiuk, 1954; Oxiuk, 1962; Lavitska & Oxiuk, 1962). More recently research has been devoted to certain particular groups of algae (Masiuk et al., 1983; Masiuk et al., 1984; Masiuk et al., 1985). The objective of the present study was to collect and analyse algae in the Kaniv reserve. A total of 45 aquatic samples and 21 soil samples were collected and examined, and 430 species were found in various waters and in soils, including 267 new records for the reserve. A new list was compiled of algal taxa collected in waters, soils and aerophytic niches in the reserve, including both bibliographic sources and the current results. It consists of 781 species, with the following composition: Cyanophyta, 115 species; Dinophyta, 5; Cryptophyta, 2; Euglenophyta, 54; Chlorophyta, 339; Bacillariophyta, 167; Chrysophyta, 6; Xanthophyta, 84; Rhodophyta, 1. The most species-rich families were Naviculaceae (94 species), Chlorellaceae (58), Oscillatoriaceae (55), Euglenaceae, Chlamydomonadaceae (48), Chlorococcaceae, Scenedesmaceae (39), Pleurochloridaceae (34), Chlorosarcinaceae (24), Nitzschiaceae (19), Characiopsidaceae (17), Chaetophoraceae (16), Tribonemataceae (15). The most species-rich genera were Chlamydomonas (38 species), Navicula (31), Scenedesmus, Oscillatoria (28 each), Cymbella (23), Chlorella, Phormidium (20 each). The research also revealed the existence of specialist aquatic algal communities in different types of water, including the Dniper river, ravine ponds and the Kaniv reservoir. The algae of the Dniper are characterized by a high diversity of Naviculaceae, Scenedesmaceae, Chlorellaceae; those in ravine ponds by diversity of the Euglenaceae and Tribonemataceae; those in the reservoir by diversity of the Desmidiaceae. Analysis using Sorensen's coefficient for comparison of communities has shown that the composition of algal species depends on the type of water present (lake, ravine pond, reservoir etc.) and, where the waters are similar, on algal communities themselves, or on specific local conditions in the water.