Red Tide Swimming Safety: What Beachgoers Should Know

On August 13, 2018, Florida’s governor declared a state of emergency in seven Gulf counties stretching from Tampa Bay toward the Everglades. The trigger was a bloom of Karenia brevis, the alga responsible for most Florida red tides, and NCCOS later estimated the bloom’s total economic impact at $2.7 billion. Blooms that big are the exception. Smaller ones return every year in the same window, and late summer is when they start.

Red Tide What Is It, and Why It Flares in Fall

Red tide, or a harmful algal bloom, is a higher-than-normal concentration of a microscopic alga. In Florida that alga is Karenia brevis, a single-celled organism found almost exclusively in the Gulf, from Mexico to Florida. It produces brevetoxins, compounds that attack the central nervous system of fish and kill them in large numbers. Wave action breaks open the cells and releases the toxins into the air, which is why the shore can smell like a fish market and your eyes can water before you reach the waterline.

FWC’s red tide records go back to the 1840s, when Spanish explorers logged fish kills near Tampa Bay. Blooms last anywhere from a few weeks to more than a year. The November 2017 to February 2019 event ran roughly fifteen months, the longest in recent memory.

Florida Red Tide Season: Late Summer Through Winter

Red tides most often form in late summer and early fall and persist through winter into spring. They develop 10 to 40 miles offshore, far from coastal pollution, and currents carry them to the beach. A single bloom can cover 10,000 square miles.

The health effects ride the wind. With onshore breezes, aerosolized brevetoxins cause coughing, sneezing, and irritation of the eyes, nose, and throat. Children, older adults, people with asthma or other chronic respiratory conditions, and anyone immunocompromised should leave the beach entirely during an active bloom. The Florida Department of Health turns FWC’s sampling data into health cautions and alerts distributed through county health departments.

The Harmful Algal Bloom Beach Guide: Check Before You Go

Checking conditions takes a minute and should be part of the routine from August through November. FWC publishes a Red Tide Current Status map with the last eight days of sampling, updated daily at 5 p.m. NOAA’s HAB forecasts predict where an active bloom will move next and guide beach and shellfish closures. If the map shows medium or high concentrations of K. brevis at your beach, stay out of the water.

Red tide is one of two water-quality reasons to check before you swim in fall. The other is runoff-driven bacteria, which spike after the first rains of the season.

Keep pets out of the water too. A dog that swims in a bloom licks brevetoxins off its fur, so wash it with fresh water and soap if it goes in. And leave recreational shellfish harvesting alone during closures: oysters and clams accumulate the toxin, and the harvest areas close for that reason.

Red Tide Skin Irritation: What Contact Does to Skin and Eyes

The FWC FAQ is one line on swimming during red tide: don’t. Blooms cause skin irritation, rashes, and burning or sore eyes, and the guidance is to not swim in or around the water. The irritation is contact-based. It hits the most exposed surfaces first, your skin and your eyes, and it tends to be worse for people with sensitive skin or open cuts.

If you do get in, rinse off with soap and fresh water, wash your swimsuit, and keep your hands away from your face until you do. Rinsing early beats soothing later, and that small habit is the whole protocol.

The bloom season is a seasonal reminder that the Gulf’s chemistry is always in motion. Ocean acidification is the slower version of the same story, thinning the oyster shells that red tide closures protect. Sustainable seaweed farming is one of the few tools that measurably buffers that coastal chemistry.

Before you pack the cooler this weekend, open the FWC map. The difference between a good beach day and an itchy, burning one is the two minutes you spend checking the dots. Late summer on the Gulf is red tide season. Swim smart, or swim another day.