California Department of Public Health logo: three likenesses of people colored blue, green, and orange  
Last Edited: 3/15/2010

Blue-green Algae

Blue-green algae (also known as cyanobacteria) are actually bacteria that grow in fresh, brackish or marine water. Individual colonies of cyanobacteria are too small to be seen, but sometimes they grow rapidly into large groups and become visible. When this happens the visible growth is called a "bloom".  A cyanobacterial bloom can cause clear water to become cloudy and take on a bright green, blue, brown or red color and may look like paint floating on the water.  As algal cells within a bloom start to die, they can give off a very bad odor, similar to a sewer leak.  Cyanobacterial blooms can be dangerous as they may block sunlight and use oxygen in the water, killing other plants and animals such as fish. Some cyanobacteria produce toxins that can poison fish and animals that drink the contaminanted water or eat the dried algae that washes up on shorelines. Lethal poisonings have occurred when cattle or dogs have consumed toxin-contaminanted water from rivers, lakes or ponds with blue-green algae blooms.

When freshwater recreational areas experience cyanobacterial blooms, people who swim, wade, water-ski or do other water-splashing activities are at risk of exposure to cyanobacterial toxins. Ingestion of drinking water contaminated with cyanobacteria  or their toxins has caused human illness such as diarrhea and vomiting to liver inflammation. Some cyanobacteria produce toxins that affect the liver, others can affect the kidneys or nervous system.  EHIB researchers have collaborated with US Centers for Disease Control scientists to conduct an exposure assessment study of  two lakes in Northern California, to get a better idea of how cyanobacterial toxins in water may get into the bodies of people who do recreational activities on these lakes, but do not use them as a drinking water source.