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

When DeSantis first ran for Governor in 2018, Florida was experiencing headline-grabbing environmental problems ranging from fish-killing red tides and toxic algae blooms to manatee die-offs and invasive species that were alarming residents and giving tourists pause. —Chris Dorsey, Forbes.com, 30 Apr. 2025

Redfish and snook are two of the most popular saltwater species in Florida, and after several years of catch-and-release only fishing because of red tides along the Gulf coast, the seasons have been reinstated. —Steve Waters, Miami Herald, 13 Apr. 2025

Rising red tide Fox News and Newsmax television studios are seen in the Fiserv Forum on the day before the Republican National Convention begins, in Milwaukee, Wisconsin, July 14, 2024. —Jacob Pramuk,lillian Rizzo, CNBC, 1 Apr. 2025

What To Know Over the past week, 50 samples of the red tide algae were found in Southwest Florida, according to the Florida Fish and Wildlife Conservation Commission, with 14 samples showing indications of a red tide bloom. —Josh Hammer, Newsweek, 17 Feb. 2025

Word History

First Known Use

1904, in the meaning defined above

Rhymes for red tide

• abide
• allied
• applied
• aside
• astride
• azide
• backside
• bankside
• bastide
• bayside
• bedside
• belied

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