The most common kind of algae that produces in freshwater are blue-green algae or cyanobacteria. They are single-celled organisms that use sunlight to make their own food and are found naturally in fresh and salt waters. Cyanobacteriaphotosyntheis like plants have similar requirements like sunlight, nutrients and carbon dioxide to grow.
If conditions are suitable then it can increase to excessive levels and form visible blooms which further leads to the poor quality of water. It causes environmental problems and heavy risk to water living organisms and human beings also.