摘要：The issues presented in this study concern a very important problem of the occurrence of cyanobacterial blooms in surface water used for water supply purposes. The objective of this study was to analyze the occurrence of cyanotoxic risk in the catchment area of the Obrzyca River (including Sławskie lake which is the beginning of the river), which is a source of drinking water for the inhabitants of Zielona Góra. In order to evaluate toxicity of cyanobacterial bloom it was conducted toxicological testing using aquatic invertebrates (Daphnia magna, Dugesia tigrina) and heterotrophic bacteria (Escherichia coli, Enterococcus faecalis, Pseudomonas fluorescens). Test samples were collected from May to October, 2012. The most toxic was a sample collected from Lake Sławskie on 20th October when cyanobacteria bloom with a predominance of Microcystis aeruginosa occurred and the amount of microcystins was the largest. The methanol extract of the sample was toxic only above a concentration of 6·103 mg·dm-3. The lethal concentration (48-h LC 50) for Daphnia magna was 3.09·103 and for Dugesia tigrina (240-h LC 50) 1.51·103 mg·dm-3 of microcystins (MC-LR, MC-YR and MC-RR). The same extract stimulated growth of Escherichia coli and Enterococcus faecalis cells.
