algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. The diversity of these HABs make them even harder to manage, and present many issues, especially to threatened coastal areas. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings. Due to their negative economic and health impacts, HABs are often carefully monitored. HAB has been proved to be harmful to humans. Humans may be exposed to toxic algae by direct consuming seafood containing toxins, swimming or other activities in water, and breathing tiny droplets in the air that contain toxins. If the HAB event results in a high enough concentration of algae the water may become discoloured or murky, varying in colour from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discolouration. See also Chironomus annularius – A species of nonbiting midges that act as a natural algae control. Thin layers (oceanography) References External links FAQ about Harmful Algal Blooms (NOAA) Algal blooms Algae Aquatic ecology Articles containing video clips Biological oceanography Environmental issues with water Water quality indicators