Concentration of toxic species of algae that cause a reddish coloration in water.
A dense growth of marine algae (dinoflagellates) in coastal waters. The tide may discolor the surface of the ocean, giving seawater a red, green, or brown appearance. The algae that cause the tide produce a variety of poisons which may kill marine vertebrates, accumulate in shellfish, and cause potential health hazards for humans who consume shellfish. Diseases associated with the consumption of shellfish during a red tide include amnesic shellfish poisoning and diarrheal shellfish poisoning, among others.