These algae, known as PHYTOPLANKTON, are single-celled protists, plant-like organisms that can form dense, visible patches near the water's surface. Certain species of phytoplankton, dinoflagellates, contain photosynthetic pigments that vary in color from green to brown to red.
When the algae are present in high concentrations, the water appears to be discolored or murky, varying in color from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discoloration, and not all discolored waters associated with algal blooms are red. Additionally, red tides are not typically associated with tidal movement of water, hence the preference among scientists to use the term algal bloom.