Harmful algal bloom in coastal areas are also often referred to as "red tides".  The term "red tide" is derived from blooms of any of several species of dinoflagellate, such as Karenia brevis. However, the term is misleading since algal blooms can widely vary in color, and growth of algae is unrelated to the tides. Not all red tides are produced by dinoflagellates. The mixotrophic ciliate Mesodinium rubrum produces non-toxic blooms coloured deep red by chloroplasts it obtains from the algae it eats.
As a technical term, it is being replaced in favor of more precise terminology, including the generic term "harmful algal bloom" for harmful species, and "algal bloom" for benign species.