The article presents an overview of the mass development of cyanobacteria (blue-green algae) in the don river of the Rostov region, which leads to the phenomenon, received in the literature the name of harmful “flowering” of water. The harmfulness of the mass development of cyanobacteria is changes in organoleptic characteristics of drinking water, which lead to the production of a large number of dangerous to human health and animal toxins, to reduce water quality, violation of the aesthetic appearance of the reservoir, the loss of useful human properties of the aquatic ecosystem and are factors of epidemic safety of public health. Experimental studies of the properties of cyanobacteria and toxins produced by blue-green algae are pre-sented. The first studies were carried out at the pilot plant on the technology of purification of flowering don water to ensure environmental safety of drinking water and public health.
