a reddish discoloration of sea waters, caused by large numbers of red dinoflagellates (esp. genera Gymnodinium and Gonyaulax) that kill fish and other organisms by releasing poisonous products
See red tide in American Heritage Dictionary 4
noun
A bloom of dinoflagellates that causes reddish discoloration of coastal ocean waters. Certain dinoflagellates of the genus Gonyamlax produce toxins that kill fish and contaminate shellfish.