The changes of distribution and infectivity of cyanophages in different time and space conditions were studied. 18 water samples were collected from August to November, 2001 and 14 species of algae were directly infected. At last, in 5 samples, cyanophage (blue green alga virus) was separated, the source of which was mainly the water sample of eutrophic ponds before temperature descendension; meanwhile, 4 strains of algae-lysin bacteria were separated. Of the 14 strains of directly infected algae, Synechococcus, Anacystis, Microcystis, Plectonema, Anabaena 7120, Chlamydomouas and Chlorella wer...