DOH-Hillsborough issues warning after September 25 sample confirms presence of harmful toxins; residents urged to take precautions.
HILLSBOROUGH COUNTY, Fla. – The Florida Department of Health in Hillsborough County (DOH-Hillsborough) has issued a health alert for Lake Thonotosassa following the detection of harmful blue-green algae toxins. The warning comes in response to a water sample collected on September 25, 2025, which confirmed the presence of the toxins.
DOH-Hillsborough is urging the public to exercise caution in and around Lake Thonotosassa to prevent exposure. Blue-green algae are a common type of bacteria in Florida’s freshwater, but rapid growth, known as a bloom, can discolor the water and produce harmful toxins.
Residents and visitors are strongly advised to adhere to the following safety precautions:
- Avoid Contact: Do not drink, swim, wade, use personal watercrafts, or come into contact with waters where a visible bloom is present. Blooms can appear as scum, foam, or paint on the water’s surface and often emit unpleasant odors.
- Keep Pets and Livestock Away: Animals should be kept away from the affected area. Waters with algae blooms are unsafe for animals, and pets and livestock should be provided with an alternative source of water.
- Post-Exposure Care: Wash skin and clothing with soap and water immediately if any contact occurs with the algae, discolored water, or water that smells unpleasant.
- Cooking and Cleaning: Do not cook or clean dishes with water contaminated by algae blooms. Health officials warn that boiling the water will not eliminate the toxins.
- Fish Consumption: Eating fillets from healthy fish caught in the lake is generally considered safe. However, individuals should rinse fillets with tap or bottled water, discard the guts, and thoroughly cook the fish. Do not eat shellfish in waters with algae blooms.
Blue-green algae blooms are often triggered by environmental factors such as sunny days, warm water temperatures, still water conditions, and excess nutrients, and are more frequent during summer and fall. The toxins produced by the algae can be harmful to humans, pets, and aquatic ecosystems. Sensitive individuals, including children, the elderly, and those who are immunocompromised, are especially at risk.
The Florida Department of Environmental Protection (DEP) and its partners continue to monitor the situation. Toxin results from collected samples can be viewed on the Protecting Florida Together or DEP’s Algal Bloom Dashboard.
Reporting and Resources
The public is encouraged to report any related issues:
- Algae Blooms: Report new blooms to DEP online or by calling 1-855-305-3903.
- Human Health Concerns: Report symptoms from exposure to the Florida Poison Information Center at 800-222-1222.
- Animal Health: Contact a veterinarian if a pet is suspected of illness after contact with contaminated water.
- Fish or Wildlife: Report dead, diseased, or abnormally behaving fish or wildlife to the Florida Fish and Wildlife Conservation Commission at 800-636-0511.
For other health questions, DOH-Hillsborough can be reached at 813-559-4065. Current water quality status and health notifications are available at Protecting Florida Together.
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