Blue-green Algae & Harmful Algae Blooms…..When in doubt, best keep out

by admin on August 30, 2014

Candlewood LakeWe have been fortunate with the weather this summer (cool nights and moderate days), which tends to minimize the occurrence of blue green algae blooms – however it’s important to be aware of the following facts.

When temperatures climb and the sun beats down, conditions are especially favorable for Connecticut lakes to produce algae blooms, some of which can be harmful to pets and humans.

What: Harmful algal blooms (HABs) are most often blue-green algal (otherwise known as cyanobacteria) blooms containing toxins or other noxious chemicals, which can pose harmful health risks.  Not all algae blooms are “blue-green” (see page 2 photos), and not all blue-green algal blooms are harmful, however there is no visual way to predict the toxicity of a blue-green algal bloom without a more detailed chemical evaluation.

Several types of blue-green algae commonly occur in lakes and ponds in Connecticut.  Blue-green algae blooms can occur frequently throughout the summer season in some lakes.  Spells of hot weather and heavy rains carrying nutrients can create conditions that increase the possibility for frequent blue-green algae blooms though they are hard to predict.  Since lakes are always in motion, the wind and waves that bring a bloom to a beach are just as capable of blowing it away.  Blooms can linger for a few hours or days depending on weather conditions.

Why is this a concern? People or pets that immerse themselves in waters when a bloom is present may be exposed to toxins.  They may develop skin irritation or upper respiratory problems from exposure to HABs, gastrointestinal problems, and in extreme cases, dogs and other animals have even died after ingesting water containing these toxins by either drinking the water or cleaning their fur coats with their tongues.

Where: Severe blue-green algal blooms typically occur on lakes when nutrient loading exceeds certain levels resulting in poor water quality and looks like green paint, pea soup, or a thick green cake (see photo gallery below for examples). These blooms may produce and release toxins.  Algal blooms often result in extremely low water clarity (less than 1 foot).

What should I do if I suspect a HAB on my lake? When blooms are present, people should avoid contact with the water and they should prevent animals from swimming in or drinking the water.  Scientists do not yet know what causes some blooms to produce toxins while others do not, so the safest course of action is to avoid contact with all blue-green blooms.

What does it look like? Blue-green algae can be hard to distinguish from other types of algae. While it’s often described as looking like pea soup or spilled green paint, it can take other forms as well.


Photo of Blue Green Algae shown above.



 The  photo above is Filamentous Algae , NOT Blue Green Algae.

 What should I do if I or my pet accidently come in contact with a blue-green algae bloom?

  • Thoroughly rinse yourself and your pet(s) 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-ingestion.


If you believe you, someone else or a pet are experiencing adverse health effects due to contact with, or ingestion of, lake water/algae, you should seek medical attention.

In addition, people are encouraged to call their local Public Health Agency, or Connecticut Department of Public Health (CDPH) (860) 509-7758. Citizens can also contact CT Department of Energy and Environmental Protection (CT DEEP) at (860) 424-3020 or visit the DEEP website for more detailed information at


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