What are Cyanobacteria? Cyanobacteria (commonly called blue green algae) are increasingly prevalent in the world’s water supplies. It can produce toxins which are harmful to human and animal health. Toxic cyanobacterial blooms occur because of favorable conditions including hot, sunny days and warm, nutrient-rich water. Cyanobacteria blooms are becoming worse due to global warming. Toxic Cyanobacteria blooms have been documented in water in 35 states and in Africa, Australia, China, and Europe. Cyanobacteria is considered a global problem.