Cyanobacteria bloom in waterbody

Cyanobacteria (also known as blue-green algae) are photosynthetic bacteria that share similar characteristics of algae. Cyanobacteria are normally present in all types of waterbodies throughout Massachusetts, including in public water system (PWS) surface water sources.  Like algae, cyanobacteria can multiply quickly in response to conditions that are favorable for their growth resulting in “blooms” that are green or blue-green in color.  Blooms often look like pea soup or as though green paint has been spilled in the water.

Cyanobacterial blooms can contribute to taste and odor issues for PWSs; however, they also have the potential to produce toxins (cyanotoxins) that can be harmful to public health.  Cyanotoxins may cause damage to the liver, kidneys, or nervous system.  Exposure to cyanobacteria and their toxins occur primarily during recreational activity through oral, dermal and inhalation routes.  Exposure may also occur through ingestion of cyanotoxin-contaminated drinking water.

Cyanobacterial blooms are primarily a concern at PWSs with surface water sources, specifically those using lakes, ponds or reservoirs.  PWSs with river intakes, groundwater or groundwater under the influence of surface water (GWUI) are not considered to be at significant risk of cyanobacteria issues at this time.  

Cyanobacteria, and the cyanotoxins they produce currently are not currently regulated by the federal government or Massachusetts. On June 17, 2015, the U.S. Environmental Protection Agency (US EPA) released 10-day drinking water (DW) health advisory (HA) levels for two cyanotoxins – microcystins and cylindrospermopsin.  HAs are non-regulatory concentrations at which adverse health effects are anticipated to occur by oral ingestion of DW over specific exposure durations.   A HA value is determined by US EPA using the best available information on health effects, exposure and other relevant data.  The US EPA HA values for the two cyanotoxins are shown below.

US EPA DW Health Advisory Table

More information regarding US EPA’s HAs for cyanotoxins is available here:

It is important to note that the Massachusetts Department of Public Health (DPH) is the state agency responsible for cyanobacteria in recreational waters and for providing advice for people and pets who may have been exposed. Please visit here: for additional information on DPH’s program.