Cyanobacteria are photosynthetic bacteria carrying chlorophylls and other pigments; their genera include Anabaena, Nostoc and Synechococcus, and they were long called blue-green algae. They thrive in nutrient-rich fresh water where they can form dense blooms. Some species produce potent toxins such as microcystins that contaminate drinking water and accumulate in fish and shellfish, posing liver and neurological risks. Water utilities and food safety authorities monitor blooms and apply treatment barriers, while edible Spirulina is cultivated under controlled conditions as a protein-rich ingredient.