Blue-Green Algae Health Risks

What is Blue-Green Algae?

Algae exists naturally in Candlewood Lake and Squantz Pond and in lakes, rivers and ponds across the globe. Some species, more commonly referred to as Blue-Green Algae, can be harmful to humans and household pets because they can produce harmful toxins. These are potentially dangerous and should be avoided when swimming, fishing or boating.

Not all algae is harmful. Under certain conditions, Blue-Green Algae can become concentrated on or near the surface, producing what is commonly known as an algae bloom. Algae blooms typically occur naturally in mid-to-late summer, due to a mix of elevated nutrient levels, such as phosphorus, lots of direct sunlight, and higher water temperatures. Algae blooms are occurring more frequently due to global climate change and continued development around water bodies which contributes to increased runoff -- adding nutrients like phosphorus to the lake every time it rains.

The only way to know for certain that an algae bloom poses a health risk is through a detailed scientific evaluation in a laboratory so caution is the most prudent advice.  

Blue-Green Algae (Potentially Harmful)
Filamentous Green Algae (Not Blue Green Algae, and Not Harmful)
Health Risks

If you or your pet comes into contact with an algae bloom, be aware of possible adverse health effects which can include skin, eye and respiratory irritation. Ingestion of enough of the algae can also cause acute gastrointestinal symptoms, including vomiting and diarrhea.

If the algae are producing toxins, symptoms can be more serious, especially for children and small pets, and can affect liver, kidney and neurological functions. Anyone who is exhibiting these symptoms who may have come into contact with water contaminated with a blue-green algae bloom should contact their doctor immediately.

Algae Treatment

If you or your pet accidentally come into contact with an algae bloom:

  • Thoroughly rinse yourself or your pet off.
  • If you experience any signs of symptoms post-exposure,contact your healthcare provider or Poison Control Center for advice.
  • Immediately contact your veterinarian if your pet shows any symptoms post-exposure.

You may also contact CT Department of Public Health 860-509-7758, or CT Department of Energy and Environmental Protection 860-424-3020, or send an email to Visit the DEEP website for more detailed information.

Algae Awareness

If you believe you see a blue-green algae bloom on Candlewood Lake, please contact the Candlewood Lake Authority at or 860-354-6928 and provide us with as much of the following information as possible:

  • Date and Time of Bloom
  • Specific Location of Bloom
  • Photo of Bloom

The CLA actively tracks and monitors the presence of Blue-Green algae in Candlewood Lake to provide an early warning system for lake users and area Town Health Departments.