The oldest chlorophyll-bearing organisms of the planet, which had lived modestly and imperceptibly for many millennia, suddenly acquired wide, but often sad, fame. Today, botanists refer to this type of plant about 1400 species of organisms. The most famous blue-green algae, which develop in large quantities in water bodies, cause "blooming" of water. In the second half of the twentieth century, this "bloom" spread especially widely and was registered in many countries of the world. The "blooming" of water in reservoirs built in the basins of lowland rivers has reached a significant scale.