Stay in the know about wildlife, water quality, and ecosystems on Sanibel and Captiva Islands and in Southwest Florida

Red Tide Impacts Continue in Lee County

February 4, 2025
red tide noaa satellite map

A red tide bloom that moved nearshore to Sanibel and Captiva last week is increasing in intensity and continues to impact the islands.

Both islands saw medium to high concentrations of the red tide organism, Karenia brevis, detected in samples from both SCCF’s Marine Laboratory and the Florida Fish & Wildlife Conservation Commission. Hundreds to thousands of dead fish have washed ashore and are scattered along the beaches.

The current bloom started near Tampa Bay shortly after Hurricane Milton in October. Recent water samples now indicate positive red tide concentrations all the way from Pinellas / Manatee Counties down to the Florida Keys.

“The main bloom source is just offshore Sanibel, and it can be moved near the shore at any time based upon currents and wind,” said Marine Lab Research Associate Mark Thompson. “The main bloom is likely very high in concentration of K. brevis and associated brevetoxins, and winds creating waves can make the toxin an airborne irritant even when concentrations are not high along the beach.”

Red Tide Health Alerts for 10 Areas Around Lee County

The Lee County Department of Health has issued red tide alerts for 10 areas in and around Lee County — Allison Hagerup Beach Park, Turner Beach, Bowman’s Beach, Gulfside City Beach Park, Tarpon Bay Road Beach, Lighthouse Beach Park, Lynn Hall Beach Park, Bonita Beach Park, and offshore Cayo Costa and Bokeelia.

red tide aerial sanibel Ralph Arwood
Aerial above Sanibel, Feb. 4, 2025. Credit: Ralph Arwood / Calusa Waterkeeper

Residents and visitors in these areas are advised to take the following precautions:

  • Do not wade or swim in or around red tide. Red tide can cause skin irritation, rashes, and burning/sore eyes.
  • Keep pets away from water and dead fish. If your pet swims in waters with red tide, wash them with soap and water as soon as possible.
  • Wash your skin and clothing with soap and fresh water if you have had recent contact with red tide, especially if your skin is easily irritated.
  • Remain cautious and stay away from these locations, especially if you have chronic respiratory conditions.
  • Residents living in affected beach areas are advised to close windows and run the air conditioner.

“There are also floating dead organisms in the water, which can carry various bacteria,” Thompson said. 

Advance our knowledge on human health impacts from red tide by volunteering for a long-term study led by SCCF’s partners at the Roskamp Institute >> 

What Causes 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 its name. 

K. brevis produces brevetoxins, which may lead to adverse health impacts for humans and potentially fatal impacts for wildlife. The severity of these impacts depends on the concentration of K. brevis cells per liter of water, with impacts to humans and wildlife becoming likely at concentrations of 10,000 and above.

While red tide occurs naturally, human activities such as the introduction of excess nutrients into waterways via watershed runoff and Lake Okeechobee releases can exacerbate an existing bloom. The Caloosahatchee River and Estuary has been receiving water from Lake Okeechobee for several months under Lake Okeechobee Recovery Operations, and average flows have remained in the optimum flow envelope for estuary health. SCCF staff provide regular updates and recommendations to water managers and decision makers through our Caloosahatchee Conditions Reports

SCCF will continue to monitor the bloom — sign up for our Weekly Water Conditions Tracker to stay informed. 

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