Scientific names:  AnabaenaAphanizomenon, and Microcystis, etc.


Physical characteristics

  • can be unicellular, filamentous (thin and stringy or hair-like), or colonial
  • buoyant and will form “scum” layer or floating mats on water surface
  • can cause blue, green, brown, or reddish-purple coloration of water


Where does it grow?

Blue-green algae can grow in both marine and freshwater. Most of the harmful algae blooms (HABs) occur in freshwater. Blue-green algae can grow in lakes, ponds, reservoirs, and slow-moving streams when environmental conditions are right, such as warm water, abundance of nutrients like phosphorus or nitrogen, and plenty of sunlight.


Cons of Blue-green algae (there are no Pros)

Blue-green algae produce cyanotoxins as well as taste-and-odor compounds that fowl the water they are found in. The cyanotoxins can pose a serious threat to not only fish but livestock, companion animals, and humans as well.


USDA, NRCS. 2018. The PLANTS Database (, 28 March 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.


Information and photos courtesy of AquaPlant A Diagnostics Tool for Pond Plants and Algae.