There are many different aquatic organisms that have historically been called “algae.” Though there are some similarities in the different forms of “algae” (they are aquatic and can photosynthesize), these organisms have a wide range of physical attributes. Our scientific understanding of these organisms has increased through time, and we now recognize the term “algae” as a non-scientific description of organisms that are not necessarily related.
“Blue-green algae” are actually bacteria and are thus even more distinct from other types of algae. Blue-green algae are simple aquatic organisms that exist naturally in marine and freshwater waters, rivers, lakes, and ponds. When they are present in low numbers, they are a normal part of a healthy ecosystem.