Cyanobacteria, also known as bluegreen algae, are actually more closely related to bacteria than to algae. These ancient organisms are found among the first fossilized signs of life preserved in rocks on earth and species have persisted up to the present in a variety of wet or humid habitats. They are similar in size to algae, and like algae, can convert light in the presence of the pigment chlorophyll to carry out photosynthesis, capturing energy by making sugars for cell growth and metabolism. Cyanobacteria also have other special pigments that aid in photosynthesis, which can turn them a variety of colors, including blue-green, bright green, brown, olive green, reddish-brown and maroon.
The bluegreen genera Anabaena, Aphanizomenon and Microcystis are among the most commonly found bluegreens in lakes of the Puget lowlands during the summer. All three can produce toxins on occasion that may cause liver or neurological damage to mammals. The toxins stay inside the cells until released by cell death or rupture. This toxicity can remain in lake water from a few days to a week after a bloom disappears.
Signs of toxic damage to the liver include jaundice, shock, abdominal pain and severe thirst; while signs of neurological toxins include staggering, paralysis and involuntary muscle movement. Both types of toxins have been reported to kill fish, waterfowl and animals. No confirmed human deaths in the United States have been reported from contact with a toxic bloom, but skin irritation and gastroenteritis have been documented.
The mere presence of cyanobacteria does not mean toxicconditions are present, as most blooms appear not to produce the toxins or only in trace amounts. However, there is no change in appearance between a toxic and nontoxic bloom. Specific testing must be completed to make the determination as to whether or not a bloom presents a health and safety risk. Because of the expense, toxicity testing is often limited to those lakes where other signs of toxicity have been observed. Studies are underway to understand whether environmental conditions or genetic background are better determinants of what causes the cyanobacteria to produce toxins.