The distribution of algae was investigated at 5 reservoirs located in Kyonggi-Do. Blue-green algae such as Oscillatoria and Microcystis which are pollution indicators and water-bloom causing agents were dominant in the eutrophic waters. In order to develop a method for using cyanophage as biological controller of eutrophication, 7 strains of filamentous cyanobacteria and 1 strains of unicellular blue-green algae were isolated on the BG-11 solid medium added with 50㎍/ml cycloheximide, 50㎍/ml nystatin, and 10㎍/ml germanium dioxide (GeO_2).