What is Red Tide?

Karenia brevis is a single-celled organism belonging to a group of algae called dinoflagellates. Large concentrations of this organism, called blooms or ‘red tides,’ can discolor water red to brown, giving it the colloquial name. Karenia brevis occurs in marine and estuarine waters of Florida and typically blooms in the late summer or early fall. Blooms develop offshore and are brought inshore by currents and winds, usually in bottom waters. Although there is no direct link between nutrients related to human activity such as sewage and runoff on the initiation of blooms, once blooms are transported inshore, these nutrient sources can fuel them. Karenia brevis produces neurotoxins called brevetoxins that can sicken or kill fish, seabirds, turtles, and marine mammals. Although less common, blooms of K. brevis can also contribute to fish kills by depleting the water of dissolved oxygen. Toxins can also affect humans, causing respiratory irritation if aerosolized toxins are inhaled, skin and/or eye irritation by contact or shellfish poisoning if shellfish contaminated with toxins are consumed.

Source: FWC Fact Sheet


Call the Florida Department of Health Poison Hotline at 800-222-1222 with questions related to the health impacts from Red Tide.

If you experience symptoms related to red tide, these are the ICD-10 Codes to request that medical professionals use to help the CDC and Florida Department of Health track public health impacts.

T65.82 Harmful Algal Bloom (HAB) exposure in general

T65.84A - Initial HAB exposure - (Red Tide or cyanotoxin from blue-green algae)

Z77.121 - After the fact exposure, including longer-term effects from contact with HABs or toxic algae bloom