Cyanobacteria are microscopic, photosynthetic organisms that are found naturally in all aquatic environments. Under certain conditions, cyanobacteria can multiply and become very abundant, discoloring the water throughout a water body or accumulating at the surface; these occurrences are known as blooms. This ITRC guidance discusses key aspects of harmful cyanobacterial blooms management that waterbody managers and other interested parties should consider as they respond to these events.