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 Cyanobacteria?

  • Cyanobacteria (blue-green algae), are microscopic organisms found in all types of water usually in the warm summer and early Fall months.
  • The bacteria live in fresh, combined salt and fresh water, and ocean water. Their food comes from an environment rich in phosphorous and nitrogen.
  • The bacteria grow quickly into blooms that spread across water surfaces and can look like blue, bright green, brown, or red scum, foam, or mats.

What are possible health effects associated with Cyanobacteria?

  • The bacteria toxins are powerful natural poisons and harmful to all living things
  • Avoid going into or drinking from scummy water with colorful blooms.
  • People and animals that come into contact with these blooms by swimming in or drinking the water should rinse off with fresh water immediately.
  • Contact a healthcare provider for humans or veterinarian for a pet if exposed

How you can help with this issue?

The existence of cyanobacteria in water sources is expected to increase as our climate gets warmer. Learn to recognize the signs of this toxic poison.

  • Contact your local public health department to report the location of possible cyanobacteria contamination and they will follow up.
  • Maintain and pump your septic system every three years to prevent leaks. etc.
  • Use fertilizer according to label instructions to reduce runoff (excess nitrogen and phosphorous) into the environment.
  • Tell others about harm from cyanobacteria so they are aware when out near ponds or lakes.

Who should I contact if I see a potential Cyanobacteria?

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

Local Pictures of Cyanobacteria

Cyano wellfleet

cyano wellfleet 3cyano wellfleet 2Helpful 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 

Cyanobacteria Fact Sheet with Pictures from Wellfleet

1 Taken from the CDC page