“In 1989, the first toxic cyanobacterial bloom west of the Cascade Mountains was documented in American Lake, Pierce County. In 1999, the city of Bremerton first acknowledged the problem in Kitsap Lake. By August of 2019, 48 of 50 states have reported cyanobacteria bloom events.” – Washington Department of Health
Cyanobacteria, also known as “blue-green algae”, are a group of photosynthetic bacteria, some of which are nitrogen-fixing, that live in a wide variety of moist soils and water either freely or in a symbiotic relationship with plants or lichen-forming fungi. Colonies may form filaments, sheets, or even hollow spheres. Many forms exist. The normal(sic), photosynthetic cells that are formed under favorable growing conditions; akinetes – climate-resistant spores that may form when environmental conditions become harsh; and thick-walled heterocysts which contain the enzyme nitrogenase, vital for nitrogen fixation in an anaerobic environment due to its sensitivity to oxygen.
Cyanobacteria have an extensive fossil record – the oldest known fossils are found in rocks of Western Australia, dated 3.5 billion years old, back to the beginnings of life on Earth and before the evolutionary separation animals, plants, and fungi.
Many unicellular cyanobacteria grow in colonies that are often surrounded by a gelatinous or mucilaginous sheath – a biofilm – that allows them to share their form of respiration or electron-transfer without oxygen, whereas others grow as thread-like filaments. Morphologies in the group have remained much the same for billions of years.
Factors needed for bloom formation – whether toxic to other forms of life or not – are complex. Researchers have investigated factors such as light, temperature, percent oxygen saturation, nutrient availability and depletion, wind patterns, internal lake mixing, growth stage and zooplankton predation.
Three genera of cyanobacteria account for the vast majority of blooms: Microcystis, Anabaena, and Aphanizomenon. A bloom can consist of one or a mixture of two or more genera of cyanobacteria. Cyanobacteria cannot maintain an abnormally high population for long and will rapidly die and disappear after 1-2 weeks. If conditions remain favorable, another bloom can replace the previous one in such a way that it may appear as if one continuous bloom occurs for up to several months.