<P> Red tide is a common name for a phenomenon known as an algal bloom (large concentrations of aquatic microorganisms) when it is caused by a few species of dinoflagellates and the bloom takes on a red or brown color . Red tides are events in which estuarine, marine, or fresh water algae accumulate rapidly in the water column, resulting in coloration of the surface water . It is usually found in coastal areas . </P> <P> These algae, a form of phytoplankton, are single - celled protists, plant - like organisms that can form dense, visible patches near the water's surface . </P>

Which group of organisms is most commonly responsible for red tides