Blue-green algae (BGA) are cyanobacteria, microscopic organisms that can photosynthesize. They are found in the summer plankton of many lakes. When conditions are favorable, the number of BGA can increase dramatically, or “bloom.” These blooms may be visible as a floating scum that resembles paint on the surface of the water.
Warm, calm water with elevated nutrients (primarily phosphorus) make algae grow faster than normal, contributing to algae blooms. As long as nutrients are in excess, algae can grow until some other factor, often light or temperature, limits their growth. Some of the sources of phosphorus that promote BGA blooms are from fertilizer runoff, decomposing vegetation, soil erosion, and septic tank leaching.
In addition to potential toxins (which have no known antidotes), BGA can have many other negative affects.