red tide

noun
  1. a brownish-red discoloration of marine waters caused by the presence of enormous numbers of certain microscopic flagellates, especially the dinoflagellates, that often produce a potent neurotoxin that accumulates in the tissues of shellfish, making them poisonous when eaten by humans and other vertebrates.

Origin of red tide

First recorded in 1900–05
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for red tide

red tide

noun
  1. a discoloration of sea water caused by an explosive growth in phytoplankton density: sometimes toxic to fish life and, through accumulation in shellfish, to humans
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

red tide in Science

red tide

  1. A population explosion of certain species of dinoflagellates, a kind of protozoan found in plankton. The dinoflagellates color the water red or reddish-brown and secrete a toxin that kills fish. Red tide usually occurs in warm coastal waters.
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