The present invention relates to an industrial strain of unicellular green alga Parachlorella nurekis 1904 KIEG, deposited in the Culture Collection of Algae and Protozoa (CCAP), Scottish Marine Institute, Dunbeg, OBAN, Argyll, PA37 1QA, UK, under number CCAP 259/1, and its use for killing blue green algae, bacteria and fungi.