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Harmful Algal Blooms 

Algae and cyanobacteria (also called blue-green algae) are plant-like organisms that live in water.
They can quickly grow out of control, or "bloom."
Some of these blooms produce toxins (poisons) that make people and animals sick.

Harmful algal blooms can look like foam, scum, mats, or paint on the surface of the water.
They can also grow underneath the water, making some harmful algal blooms hard to see.

Not all blooms are harmful. Blooms can harm people, animals, or the environment if they:

  • Make toxins

  • Become too dense

  • Use up oxygen in the water

  • Release harmful gases

Algae and cyanobacteria occur naturally in water.
They are more likely to grow into a harmful algal bloom when water is:
 

  • Warm

  • Slow-moving

  • Full of nutrients, such as nitrogen or phosphorous

 

Nutrients get into water when fertilizer, sewage, or runoff from cities and industrial buildings washes into lakes, rivers, or oceans.
This can happen during rainstorms, for example.

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To help ensure that your day at the beach doesn’t result in illness related to poor water quality,
Chatham Health District conducts weekly beach water testing between Memorial Day and Labor Day.
Water samples are tested at the CT Public Health Laboratory for E.coli. 
Visual observations are documented for cyanobacteria (Blue-Green Algae) at locations known to be at high risk for harmful blooms.

We follow the Guidelines for Monitoring Swimming Water and Closure from CT Department of Health and CT Department of Energy and Environmental Protection to determine if and when a swimming area needs to be closed.   

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​​Learn more about harmful Algal Blooms from CDC HERE

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Visit the Chatham Health District Beach Status Dashboard 

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