Cyanobacteria in Freshwater Ponds

Cyanobacteria genus Dolichospermum

Close-up of Cyanobacteria genus Dolichospermum

Mares Pond cyanobacteria

Example of a cyanobacteria bloom

Current Water Bodies with Cyanobacteria Advisories in Falmouth (as of 7/15/21):

  • Ashumet Pond

  • Cedar Lake

Falmouth Cyanobacteria Sampling Report - 7/13/21


About Cyanobacteria

Cyanobacteria, also referred to as blue-green algae, are commonly found in the phytoplankton community of aquatic ecosystems.  They form the base of the food web of freshwater ponds and streams that flow into coastal estuaries and the ocean but occasionally they grow rapidly in fresh water and form scums or mats in the water. Some blooms can produce toxins harmful to people and animals. Blooms on Cape Cod are most common in summer and early fall. Cyanobacteria blooms can change the water’s appearance from slightly discolored to resembling pea soup or thick paint. Blooms frequently appear blue or green but could be another color, such as brown or red. These blooms can also give the water a bad odor or taste. Health concerns from cyanobacteria blooms and their toxins include skin and eye irritation from topical exposure to gastrointestinal symptoms, liver damage and neurological damage when large amounts of toxins are ingested.

If you see water that appears to have an algae-type bloom, do not come into contact with or ingest the water. Prevent contact and ingestion by children and pets and contact the Falmouth Health Department so it can be investigated.

Causes of Harmful Cyanobacteria Blooms:

Harmful levels of Cyanobacteria, referred to as blooms, can be caused by a combination of factors including warm water temperatures and high nutrient levels from sources such as fertilizer, human waste from leaking septic systems, stormwater runoff and pet and wildlife waste.

Please refer to the following links for more information:  

Association to Preserve Cape Cod:
https://apcc.org/our-work/science/community-science/cyanobacteria (Includes map showing test results for a limited number of Cape ponds)

Mass.gov
https://www.mass.gov/info-details/guidelines-for-cyanobacteria-in-freshwater-recreational-water-bodies

https://www.mass.gov/service-details/identifying-cyanobacterial-blooms-and-scums-photographs-of-blooms-and-scums

Algae bloom without scum

Example of an algae bloom without scum

Algae bloom with scum layer

Example of an algae bloom with scum