In the countries of the former USSR, where many reservoirs are created on flat rivers, a shallow water problem arose. Their area is already about 1 million hectares. In fact, shallow water does not play a significant role in the accumulation of water reserves. But they are occupied by extensive agricultural land, they podtaplivayut surrounding land. In the Kiev Sea, up to 40 ... 50% of the water mirror is in shallow water. The shoals, and then the reservoirs in general, became the arena of invasion of microscopic plants - blue-green algae. By the damage they cause, these tiny organisms are no better than the toothy Brazilian piranhas. Of the hundreds of species of blue-green algae, nine cause
the strongest pollution, called the flowering of water. Large-scale  regulation of the largest rivers, in particular the Dnieper and the  Volga, has created unlimited opportunities for the flowering of water. The  ideal habitat of blue-green algae is extensive, well warmed by the sun,  weakly flowing shallows, enriched with phosphorus and nitrogen organic  substances contained in rainwater washouts from the soil. It is these conditions that these algae found in the water bodies of the regulated rivers.
Sometimes microscopic algae reproduce so violently that the entire reservoir is tightened by a mucous membrane.
When  they die, blue-green algae bring a real disaster: phenols, indole,  skatole, other poisonous substances and their decomposition products  enter the water in large quantities. Fish  leave such water bodies, the water in them becomes unsuitable even for  recreational (Latin recreatio letters - rest, recreation, restoration of  human forces expended in the process of labor) goals. In  the Institute of Hydrobiology of the Academy of Sciences of Ukraine, a  method has been developed for purging oxygen through the water column  contaminated by them. Applied and special pesticides that kill aquatic life.
Under  the influence of mineral coagulants, which are also used for  clarification and purification of water flowing into the water supply  network, the algae irreversibly coalesce into lumps. Viruses are found for which blue-green algae are a desired dish.
The  extraction of algae from water is promising, after which they are used  as fertilizers for fields or as industrial raw materials, because these  algae contain up to 50% protein, a large amount of vitamin B12 and other  valuable components. It is established that reed, cattail, and reed release phytoncides, toxic for these algae. Particularly strongly oppresses their development hornwort immersed.