Cyanobacteria Monitoring Map

The 2021 cyanobacteria monitoring program came to a close for the season as of mid-November and will resume end of May 2022. Thank you to our partners and volunteers who help make this pond program successful.

Click here (PDF) for the list of ponds monitored in 2021.

Remember, if you notice pond water is scummy, or discolored and may have a strong odor, avoid contact. If you see what you think might be a suspicious cyanobacteria bloom, notify your local health department and send a photo to noting the location, day and time.

How to use the map:

Pan around the map and zoom in/out to locate an area or specific pond you are interested in.
Use the legend by clicking the arrow on the upper left corner of the map window to identify the cyanobacteria status of the pond you are interested in.
Click on a pond to open a pop-up box with more info about our monitoring results. If the pond you are interested in is not colored and the pop-up box does not offer recent information this means it has not been sampled recently.
For more information about what the results mean, select from the list of terms below for definitions.
If you have witnessed a possible cyanobacteria bloom or other related event at a pond that is not included on this map, please follow the instructions in the box below titled, “WHAT TO DO IF YOU SEE A POSSIBLE CYANOBACTERIA BLOOM.”

Definition of Terms


Name of the lake or pond selected. Note that lakes and ponds may have multiple names. The name listed is the most commonly used.

Cyano Status Moderate

Monitoring results indicate moderately high levels of cyanobacteria concentrations detected. While these conditions pose low to minimal health risks to adults, they can be dangerous for children or pets if water is ingested accidentally or incidentally during recreational activities. Pet exposure can be from drinking pond water or grooming after swimming. Due to lower body masses, children and pets are more susceptible to impacts at lower concentrations than adults. This tier is consistent with the town of Barnstable’s “Pet Advisory.” Map color is yellow.

Sample Location

The location of sample collection on or around the pond. Note that samples collected by boat are classified as “Pond Center” and are from the deepest point in the pond and not necessarily the geographic center. Samples collected at the shoreline are roughly indicated by North, South, East or West. It’s important to note that floating cyanobacteria are easily moved by the wind and tend to congregate on windward shorelines.


Indicates which type of cyanobacteria is most abundant in a given sample. A “mixed” dominance sample indicates roughly equal abundance of different types. This information is important because different types of cyanobacteria produce different types of cyanotoxins at different rates.

Possible Pet Health Effects

Pet exposure can be from drinking pond water or grooming after swimming. Due to lower body masses, pets are more susceptible to impacts at lower concentrations than adult humans. Pets exposed to suspected cyanotoxins should be rapidly assessed by a veterinarian.


The town in which the pond exists. If the pond is within more than one town, the town indicated is the one where the sample was collected.

Cyano Status High

Monitoring results indicate high levels of cyanobacteria concentrations detected. Health risk to adults is high and is especially dangerous for children and pets when ingested. APCC found cyanobacteria concentrations near or exceeding state recreational standards with potential for exponential growth rates of cyanobacteria. Any accidental consumption of pond water is considered dangerous and interacting with the pond in general carries risk for adverse health effects.

Use restriction pending (map color is light red) – based on APCC’s findings we have recommended a restriction and the decision to issue a restriction is pending with the town/DCR. Further information should be sought from the relevant town. Click here for contacts.

Use restriction in place (map color is dark red)- the town / DCR has issued a use restriction.

Water Temp F

This reading is the temperature of water at the pond surface at the sample location. All temperature data provided here is recorded in degrees Fahrenheit.

Two Common Types of Cyanobacteria

Dolichospermum – A genus of cyanobacteria very common in Cape Cod ponds. It can produce hepatotoxins, dermatoxins, and neurotoxins, but is known to produce Microcystin at relatively low levels.

Microcystis – A genus of cyanobacteria that is common in Cape Cod ponds. It can produce hepatotoxins, dermatoxins, and neurotoxins, but is known to produce Microcystin at relatively high levels.

Cyano Status Low

Monitoring results indicate no or low concentrations of cyanobacteria detected. To the best of our knowledge at the time and location of sample collection, regular recreational usage of the pond is safe with respect to cyanobacteria and toxins. Map color is blue.

Sample Date

The date the sample was taken.


A visible material is present as a dispersed or dense floating layer on the pond surface, or as scum washed up on the shoreline at the water’s edge. A visible cyanobacteria scum can indicate high toxin levels in the pond and the state recommends avoiding contact with the pond for a minimum of two weeks after a cyanobacteria sum has formed. Ponds appearing as red on the map indicate APCC has found a cyanobacteria scum. Other types of scum can be caused by pollen or algae in which case APCC labels them as such in the notes section to avoid confusion. If you ever find a scum with a blue-green tinge near the shore of your pond, take a picture and inform your town health department and APCC at

Common Toxins Produced by Cyanobacteria

Dermatoxin – A toxin that is a skin irritant. The most commonly occurring dermatoxin, lipopolysaccharide, is unregulated by the state.

Hepatotoxin – A toxin that can cause liver damage.

Microcystin – A type of hepatotoxin that can cause liver damage and is the primary cyanotoxin regulated by the Massachusetts Department of Public Health.

Neurotoxin – A toxin that can cause neurological damage. Anatoxin and beta-N-methyl amino-L-alanine (BMAA) are known neurotoxins that are unregulated by the state, but are currently being studied by cyanobacteria researchers.

The data and guidance depicted on this map reflect the results of APCC’s cyanobacteria monitoring methodology that measures cyanobacteria pigments in algal scums and concentrated pond water samples. Using concentrated samples is a conservative (i.e., protective) approach that helps to identify toxin-producing cyanobacteria that may concentrate in algal scums near the shoreline where most human and pet exposures occur. APCC’s use of cyanobacteria pigments as an indicator of cyanobacteria biomass and potential cyanobacteria toxin is based on published methods and leading-edge procedures originally developed by our partners at the University of New Hampshire and approved by EPA for the Cyanobacteria Monitoring Collaborative. The use of cyanobacteria pigments as an indicator of cyanobacteria biomass and potential toxins is complementary to the state Department of Public Health’s use of cell counts for the same purpose, and is a fast and precise method. The warning tiers used by APCC are based on state and federal guidance and recommendations. APCC’s data provides town health officials with precise measurements of cyanobacteria biomass at sampling locations, providing them with one type of science-based information which they may take into consideration in determining if a pond use advisory is warranted. As towns alone have the legal authority to issue and remove use advisories, the public is advised to consult their town to determine if a formal use advisory has been issued. APCC does not post advisories but provides our guidance as a service to the public so that individuals may make their own informed decisions about contact with water resources impacted by cyanobacteria blooms.

Photo Gallery

What Are Cyanobacteria?

Cyanobacteria 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. The presence of cyanobacteria is natural and important!

However, overabundant cyanobacterial growth (called blooms) and their release of dangerous amounts of cyanotoxins appear to be occurring more frequently. This is due to warming global temperatures and excessive nutrients in our ponds. This excessive growth of cyanobacteria and formation of blooms degrades habitats and damages the environment. Exposure to cyanotoxins can have serious health implications for wildlife, humans, and pets.

In spring of 2017, APCC initiated a program of monitoring in response to apparent gaps in town and state capacity to monitor freshwater ponds across Cape Cod for cyanobacteria with sufficient frequency to protect public health. The program was developed working closely with scientists at the University of New Hampshire.

APCC’s regional program monitors the formation and occurrence of harmful cyanobacteria blooms (HCBs) in freshwater ponds across the Cape. The program is made possible because of the scientific work of the University of New Hampshire, and the assistance and cooperation of towns, citizen groups, volunteers and other local organizations. Goals of APCC’s program are to:

  • raise public awareness of the issue to improve safety
  • motivate behavioral changes to reduce sources of the issue
  • monitor priority ponds across the Cape and alert appropriate town departments and the public when potentially hazardous conditions exist
  • advocate for increased attention to the issue through municipal and state political pathways.

What to do if you see a possible cyanobacteria bloom:

  1. Avoid contact and don’t let your dogs or children near the water.
  2. Take photos and make note of pond name, date, time, and location of the possible bloom.
  3. Report your observations to the local town department of health or natural resources.
  4. Inform APCC by emailing the above info about the possible bloom to so we can consider adding the pond to our monitoring program if it’s not already included.

Information and Resources:

Following are some links to various agencies who provide more information about cyanobacteria, harmful cyanobacteria blooms (HCBs) and cyanotoxins.

Massachusetts Department of Public Health
Center for Disease Control
U.S. Environmental Protection Agency
Cyanobacteria Monitoring Collaborative
University of New Hampshire – Phycokey
University of New Hampshire – Dirty Dozen

Program Partners

Town of Barnstable MASS Seal
Town of Brewster MASS Seal
Town of Chatham MASS Seal
Town of Wellfleet
Town of Yarmouth
Town of Falmouth
Town of Mashpee
Town of Harwich Seal
Town of Sandwich Seal
Town of Orleans Seal
Town of Truro Seal
Town of Provincetown Seal
United States Environmental Protection Agency
Falmouth Water Stewards
Friends of Chatham Waterways
Brewster Pond Coalition
Center for Freshwater Biology

Funding generously provided by:

Mary-Louise & Ruth N. Eddy Foundation, Cape Cod Foundation-The Falmouth Fund, Cape Cod Healthcare, Gannett Foundation and Massachusetts Environmental Trust (MET).

This project is supported in part by a grant from the Massachusetts Environmental Trust. The Trust obtains funding for grants from the sales of environmental license plates. For more information regarding the Trust, visit For information on obtaining an environmental license plate, contact the Trust at, or visit the Registry of Motor Vehicle’s website at