If you’ve ever stepped onto a Florida beach only to be greeted by stinging eyes, a scratchy throat, and a coastline littered with dead fish—you’ve probably met Karenia brevis, the microscopic culprit behind our region’s most notorious natural event: red tide.
But red tide isn’t just a headline or a smell. It’s a living phenomenon—complex, recurring, and deeply tied to the rhythms (and disruptions) of coastal Florida.
In this post, I’ll walk you through what red tide is, what causes it, how to recognize it, and what it means for beachcombers, wildlife, and nature writers like me.
What Exactly Is Red Tide?
Red tide is a harmful algal bloom (HAB) caused by Karenia brevis, a species of single-celled marine dinoflagellate that occurs naturally in the Gulf of Mexico. When conditions are just right—warm water, low salinity, nutrient overload—these tiny organisms multiply rapidly, coloring the water in reddish, rust-toned streaks.
Despite the name, red tide isn’t always red. It can look brown, orange, or even green, depending on the density and light. And sometimes, you don’t see it—you just feel it.
Why Does It Make Us Cough?
Karenia brevis releases a neurotoxin called brevetoxin, which becomes airborne when waves break and send tiny droplets into the air. For people with asthma, allergies, or sensitive lungs, this can trigger coughing, throat irritation, and even difficulty breathing.
If I smell something like a cross between low tide and burning pepper, I know to check the current bloom status before heading out.
What About the Fish Kills?
One of the most visible (and heartbreaking) effects of red tide is mass marine die-off. The brevetoxins attack the nervous systems of fish and shellfish, leading to sudden widespread deaths that can blanket beaches with decay.
In severe blooms, sea turtles, dolphins, manatees, and seabirds can also be affected—directly through exposure or indirectly by eating contaminated prey.
As a beachcomber, I’ve walked stretches of sand where the tide had deposited a trail of silvery stillness—anchovies, catfish, even horseshoe crabs—like a warning written in salt.
What Makes It Worse?
Red tide blooms can last weeks or even months, and while they occur naturally, human activity often amplifies them. Agricultural runoff, leaky septic systems, and nutrient-rich stormwater feed the bloom like fertilizer.
After a hurricane or heavy rainfall, blooms can intensify quickly.
Can You Still Explore During Red Tide?
Yes—but cautiously.
Check local red tide forecasts (myfwc.com) before you go.
Avoid swimming or wading in water with visible discoloration or dead fish.
Don’t collect or eat shellfish from a red tide zone.
Wear a mask if you’re sensitive to airborne toxins.
Rinse off after being near the water, especially with kids or pets.
Some days, I bring a notebook and stay back from the surf—watching, sketching, and asking questions rather than diving in.
~LS