red tide

noun

: seawater discolored by the presence of large numbers of dinoflagellates (as of the genera Karenia, Gymnodinium, and Alexandrium) which typically produce a toxin poisonous especially to many forms of marine vertebrate life and to humans who consume contaminated shellfish compare saxitoxin

Examples of red tide in a Sentence

Recent Examples on the Web

Last summer, for example, a red tide bloom released a neurotoxin called domoic acid that sickened sea lions and other marine mammals along the California coast, including in Los Angeles. —Clara Harter, Los Angeles Times, 30 Oct. 2024

Officials are also monitoring a plume of red tide off the coast, WUSF reported. —Kathryn Varn, Axios, 25 Oct. 2024

Advertisement But red tides — and coordinating biolumenescence — are unpredictable and quite fickle, according to UC San Diego’s Scripps Institution of Oceanography. —Grace Toohey, Los Angeles Times, 22 Oct. 2024

The organism that causes red tide is toxic and can affect the central nervous system of fish, often killing them. —Kinsey Crowley, USA TODAY, 7 Mar. 2024

Word History

First Known Use

1904, in the meaning defined above

Kids Definition

red tide

noun

: seawater discolored and made poisonous by the presence of large numbers of dinoflagellates

Medical Definition

red tide

noun

: a large area of seawater discolored by the presence of large numbers of dinoflagellates (as of the genera Karenia, Gymnodinium, and Alexandrium) which typically produce toxins poisonous especially to many forms of vertebrate marine life and to humans who consume contaminated shellfish

In simple terms, a red tide is a dinoflagellate population explosion, caused when certain species "bloom," or multiply many times faster than usual.

—Ellen Girardeau

Red tides, the blooms of toxic Karenia brevis algae that appear almost every year in Florida, often lasting for months and turning the ocean red, may be dangerous to asthma sufferers—even if they don't go swimming.

—Nicholas Bakalar

see brevetoxin, saxitoxin, shellfish poisoning