Blue-green Algae

Understanding algae, algae blooms – and the health risk of toxic blue-green algae blooms.


Algae exists naturally in Candlewood Lake, Squantz Pond and in other water bodies across the state, nation and around the globe. 


Not all algae, or even large concentrations of algae known as algae blooms, are harmful to humans.   These algae blooms typically occur naturally in lakes, rivers and ponds in mid-to-late summer, due to a mix of elevated nutrient levels (such as phosphorus) and favorable weather conditions resulting in higher water temperatures.  


There is also evidence that algae blooms are occurring more frequently than before, due largely to continued development around water bodies (which contributes to increased runoff) and the variability of weather conditions.

The Risk of Blue-Green Algae


However, some species of cyanobacteria, more commonly referred to as Blue-Green Algae, can produce toxins that are harmful to people and animals such as household pets.  These are potentially dangerous and should be avoided when swimming, fishing or boating.


The difficulty for users of Candlewood Lake is determining if an algae bloom poses a health risk.  The only way to know for sure is via a detailed scientific evaluation in a laboratory.  


So the best course of action for lake user is to avoid any exposure to any algae blooms just to be completely safe.  This applies especially to children and also to household pets, such as dogs, that may drink lake water contaminated with a toxic blue-green algae bloom or clean it from their fur.

Filamentous green algae (not blue-green).

Health Effects


If you come into contact with an algae bloom, be alert to any possible adverse health effects.



Contact with cyanobacteria, or Blue-Green Algae, can cause skin, eye and respiratory irritation. Ingestion of enough of the algae can 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.





If you 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 health care provider or Poison Control Center for advice.

  • Immediately contact your veterinarian if your pet shows any symptoms post-exposure.


In addition, you are encouraged to call your local Public Health Dept. or the Connecticut Department of Public Health (860) 509-7758.


Citizens can also contact CT Department of Energy and Environmental Protection at (860) 424-3020 or visit the DEEP website for more detailed information.




CLA Oversight


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.


We currently monitor water clarity/quality levels at Town Beaches and -- combined with a lake-wide mapping program -- provide current data to registered users and municipal health departments to quickly assess water conditions and water quality trends.  Satellite imaging is another tool we use to track possible contributing causes of algae blooms and compliment our early warning system.



Blue-green algae can appear blue...

...or white...

...or green...

...or yellow / brown.