U.S. Environmental Protection Agency


Date of this Version



Published in Cyanobacterial Harmful Algal Blooms: State of the Science and Research Needs, ed. H. Kenneth Hudnell (Springer, 2008).


Cyanobacteria (blue-green algae) are estimated to have evolved 3.5 billion years ago, at which time they began to add oxygen to the existing anaerobic atmosphere, actually changing the chemistry of the planet and allowing new life forms to evolve. These ubiquitous microbes are capable of tolerating desiccation, hypersalinity, hyperthermal conditions, and high ultraviolet radiation, often for extensive periods of time. Recently, cyanobacteria have responded to human alterations of aquatic environments, most notably nutrient-enhanced primary production, or eutrophication. In fact, cyanobacterial blooms are now viewed as widespread indicators of freshwater, brackish and marine eutrophication.

Due to the complex interactions between physical and ecological processes, it is difficult to point to any single, definitive cause for the development and proliferation of these blooms. In reality, cyanobacterial harmful algal blooms (CHABs) likely result from a combination of factors, including hydrology, available nutrients, sunlight, temperature, and ecosystem disturbance; any number of which must interact in precisely the right combination to create optimal conditions for growth. Thus, it should come as no surprise that successful prevention (inhibiting bloom formation through the manipulation of causative factors) and mitigation (ameliorating the effects of and/or controlling the blooms themselves) strategies for dealing with CHABs, may require correspondingly complex approaches.