Cyanobacteria Algal/Blue Green Algae Blooms

pond with cyanobacteria bloom

Harmful algal blooms are the rapid growth of algae or cyanobacteria that can cause harm to people, animals, or the local ecology. Harmful algae or cyanobacteria can look like foam, scum, paint, or mats on the surface of water and can be different colors. These blooms can produce toxins that make people and animals sick. Blooms occur in fresh water, such as lakes and rivers, and salt water, such as oceans or bays.1

What are CyanoHABs?2

When a dramatic increase in a cyanobacteria population occurs, this is called harmful algal blooms (HABs), or more accurately, cyanobacterial HABs (CyanoHABs). It often results in the waterbody turning bright green or blue-green, and forms a surface scum or a discoloration of the water column. CyanoHABs may also form a mat on the bottom sediments, which is more difficult to observe. The surface scums or discolored waters can extend several inches below the water surface, or accumulate near shorelines and in coves from onshore wind action. They often look like pea soup or spilled, blue or green paint; however, the color can also vary. CyanoHABs can cause dissolved oxygen (DO) swings that may result in plant and animal die-off, taste and odor issues, and can cause potential public health issues from the cyanotoxins they may release.

What are possible health effects associated with CyanoHABs?

Health concerns associated with CyanoHABs vary depending on the type of cyanobacteria, the route of exposure, and the amount of cyanotoxins present. Ingestion is the primary concern since ingesting small amounts of cyanobacteria or cyanotoxin can cause gastrointestinal symptoms while larger amounts may cause liver or neurological damage. Contact with cyanobacteria can cause skin or eye irritation. Inhaling water spray containing cyanobacteria can cause asthma-like symptoms. Small children and pets are more susceptible to the effects of cyanotoxins than adults.

What should I do if I see a potential CyanoHAB?

The first step an individual should take if they observe a potential CyanoHAB is to AVOID CONTACT with the affected water. While most algae are harmless, cyanobacteria can be skin irritants and some are capable of producing and releasing cyanotoxins, which can make people and animals sick. It is impossible to visually tell if a bloom is toxic or non-toxic; this can only be determined through analyses performed specifically for cyanotoxins.

Who should I contact if I see a potential CyanoHAB?

Contact the health department (508.240.5900 x3230 or, and alert them to what you have observed, along with the name and location of the waterbody. 

Helpful Links:

MA DEP - Harmful Cyanobacterial bloom advisories  (6/22/22)

CDC Information on Harmful Algal Bloom Associated Illness

CDC protect yourself and pets

CDC Cyanobacteria Blooms FAQs

MA DEP Cyanobacterial Harmful Algal Blooms & Water 

EPA Cyanobacterial Harmful Algal Blooms in Water Bodies 

EPA Storymap

APCC Cyanobacteria monitoring 

1 Taken from the CDC page

Taken from MA DEP page