However, under continuing favorable conditions blooms may last for several weeks. The formation of toxic blooms is unpredictable. The presence of bacteria may often be determined by a bluish tinge to the water. Concentrations of bacteria are often bluish green but may vary in color from dark green to brownish green depending on the total bacterial population. Also, not all cyanobacteria are poisonous, and the cyanobacteria which can generate poisonous toxins do not always do so.
Cyanobacteria congregate on or near the water surface.
Livestock and other animals are usually poisoned when they consume water containing high concentrations of the bacteria or the toxins generated by the bacteria. Ingestion of approximately one quart of heavily contaminated water has been fatal in cattle. Concentrations lethal to livestock do not usually occur on small water bodies where there is not enough wave action to concentrate the bacteria on shore. There are a number of ways to determine the presence of cyanobacteria. If concentrations of cyanobacteria are suspected in a water body, walk around to the leeward side of the water body.