The Florida Keys & Key West

Questions and Answers About Red Tide

What is Red Tide?

According to scientists at the National Oceanic and Atmospheric Administration (NOAA) National Ocean Service, red tide is a commonly used term for a harmful algal bloom (HAB) – when colonies of algae grow out of control while producing toxic effects on marine ecosystems and sometimes affecting the health of people.

Red tide is naturally occurring and develops due to a high concentration of microscopic algae (Karenia brevis), which are plant-like organisms.

Red tide has been documented along Gulf of Mexico coastal areas and in the Gulf of Mexico since the 1800s. In Florida, it was officially recorded in 1844. Florida and other coastal areas around the nation and the world can experience periods of red ride, at different saturation levels, during summer or early fall. Sometimes, red tide can affect

Is There Red Tide in the Florida Keys?

Results of water testing at locations off the the Florida Keys have revealed no presence of the microscopic algae (Karenia brevis),  among several sites monitored by the Florida Fish & Wildlife Conservation Commission, according to an interactive map on the FWC's Red Tide website.  (Updated Dec. 10, 2018)

What Are Red Tide’s Impacts?

Water, typically saltwater along beaches and in shallow bays, becomes discolored, sometimes red, light or dark green or brown. The size of an affected area is patchy, and typically changes week-to-week due to wind and weather conditions. Red tide conditions should not be confused with shallow waters’ brownish color caused by floating sargassum weed or naturally occurring seagrass on the bottom.

The organism that causes red tide produces toxins that, during events of medium and high levels of Karenia brevis, can affect the central nervous system of mammals, birds and other animals, sometimes causing them to die. Red tide is often associated with fish kills, which result from a lower level of oxygen in the water. Toxins in the air can be odorous.

How Long Can It Last?

The duration of a red tide bloom in nearshore Florida waters depends on physical and biological conditions that influence its growth and persistence. Red tide can last a few days or weeks or longer. No single factor causes it.

Sunlight, nutrients and water salinity, as well as speed and direction of wind and water currents, impact the length of time a red tide persists.

Can Red Tide Affect Humans?

Wave action near beaches can release the toxins into the air, during medium-and-high-levels  red tide events.  People exposed to airborne toxins blown ashore sometimes may experience temporary respiratory irritation with coughing, sneezing or watery eyes. Individuals with more sensitive conditions (emphysema, asthma or bronchitis) should avoid areas with red tide.

Is It Safe to Swim?

Yes, for most people, especially when red tide is present in low or very low concentrations. Individuals with sensitivities or susceptibility to plant products should avoid red tide waters. During significant red tide events, health officials will post cautionary signs at public beaches and NOAA weather resources will issue beach hazards advisories.

Is It Okay to Eat Seafood During Red Tide Events?

Commercial seafood available from local restaurants and seafood markets is regularly tested for safety and strictly regulated. Seafood served in restaurants and hotels is monitored and safe to eat. When certain species are not safe, advisories are issued by the Florida Fish and Wildlife Conservation Commission (FWC). It is never safe to eat dead fish that might be found floating, whether they have been subjected to red tide or not.

Where Can I Get More Information?

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