What Is Red Tide?

NOAA says the Florida red tide is caused by Karenia brevis, a type of algae that produces potent neurotoxins, and that red tides along the Florida and Texas coasts are primarily caused by this species. The Florida Department of Health in Gulf County says red tide typically forms naturally offshore, commonly in late summer or early fall, and is carried into coastal waters by winds and currents. CDC says dinoflagellates or diatoms are the most common causes of harmful algal blooms in salt water, while cyanobacteria are the most common cause in fresh water.

Breathing it is the main beach concern. NOAA says the toxins can be suspended in the air near beaches and cause human respiratory illness, and that red tide can irritate eyes and lungs, more severely for people with preexisting respiratory conditions such as asthma. Florida DOH in Gulf County says wind and wave action can break open the cells and release toxins into the air, causing eye, skin and respiratory irritation. Florida DOH in Sarasota County has said some people may have mild, short-lived eye, nose and throat irritation, and that symptoms usually stop when a person leaves the beach or goes indoors.

It also affects seafood. NOAA says the toxins can accumulate in shellfish and cause Neurotoxic Shellfish Poisoning in humans, so affected states closely monitor shellfish and may close harvesting. The Florida Fish and Wildlife Conservation Commission publishes statewide status updates, and on September 11, 2026 it reported that Karenia brevis was not observed in samples collected statewide over the past week.