HILLSBOROUGH COUNTY, Fla. – Health officials in Hillsborough County are urging the public to stay out of Lake Thonotosassa following the discovery of harmful blue-green algae toxins. The Florida Department of Health (DOH-Hillsborough) issued a formal health alert on Monday, March 16, 2026, after water samples taken late last week confirmed the presence of the bacteria.
The alert was triggered by a specific water sample collected on March 12. Local authorities are now advising residents and visitors to avoid any activity that involves direct contact with the water, including swimming, wading, or using personal watercraft.
“Do not drink, swim, wade, use personal watercrafts, or come into contact with waters where there is a visible bloom,” the department stated in its release. Officials also warned that boiling the water is ineffective, as it does not eliminate the toxins.
Blue-green algae, a type of bacteria common in Florida’s freshwater, can grow rapidly under sunny, warm, and still conditions. These blooms often appear as scum, foam, or a paint-like slick on the water’s surface and can emit a foul odor. While the algae is a natural occurrence, it can produce toxins that are dangerous to humans, livestock, and pets.
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To stay safe, the DOH recommends that anyone who comes into contact with the water wash their skin and clothing immediately with soap and clean water. Pet owners are cautioned to keep animals away from the lake entirely, as the water is not safe for consumption or bathing.
While the toxins make shellfish from the lake unsafe to eat, the department noted that “eating fillets from healthy fish caught in freshwater lakes experiencing blooms is safe,” provided the fish are rinsed with fresh water, gutted, and cooked thoroughly.
The Florida Department of Environmental Protection (DEP) is continuing to monitor the situation. Residents can track the status of the bloom through the DEP’s Algal Bloom Dashboard. If you or your pets feel ill after contact with the lake, officials recommend contacting the Florida Poison Information Center or a veterinarian immediately.
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