An algae bloom showing the bright green results of cyanobacteria. Cyanobacteria is a phylum of bacteria that obtain their energy through photosynthesis. Aquatic cyanobacteria are known for their extensive and highly visible blooms that can form in both freshwater and marine environments. The blooms can have the appearance of blue-green paint or scum. These blooms can be toxic, and frequently lead to the closure of recreational waters when spotted.