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What are HABs?

A Harmful Algal Bloom (HAB) occurs when certain kinds of microscopic organisms in a waterbody or waterway produce toxins or other chemical compounds in concentrations that can harm people, pets, or other animals.  The microscopic organisms that most commonly cause HABs in Pennsylvania are known as cyanobacteria or blue-green algae.

Cyanobacteria are a natural part of many aquatic ecosystems, but some kinds of cyanobacteria can produce toxins known as cyanotoxins.  In high enough concentrations, cyanotoxins can be harmful to people, pets, fish, shellfish, and other animals that come in contact with or ingest the toxins.

Let’s break it down:

Harmful Algal Blooms

Harmful: HABs produce toxins, known as cyanotoxins, and other chemical compounds that can harm people and animals. 

Algal: HABs are made up of microscopic organisms known as cyanobacteria or “blue-green algae.”  

Bloom: HABs occur when cyanobacteria undergo a period of rapid growth in a waterbody or waterway, often associated with abundant nutrients, water temperatures, and calm water.  


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