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.

Working with towns, citizen groups, volunteers, and other local organizations, APCC has developed a regional program to monitor the formation and occurrence of harmful cyanobacteria blooms (HCBs) and release of dangerous cyanotoxins. 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.

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

Town: The name of the town within which the pond exists. If the pond crosses multiple town lines, then the town indicated in the pop-up box is the one where the sample was collected. This can also be confirmed by referring to the “Sample Location” line in the pop-up box.

Sample Date: The date of sample collection.

Sample Location: The location of sample collection on or around the pond. Note that samples collected by boat will all be classified as “Pond Center” although generally samples collected by boat are collected at the deepest point in the pond, which often is not at the pond center. Location of samples collected from shore are indicated roughly using the four cardinal directions. It’s important to note that floating cyanobacteria are easily moved by the wind and tend to congregate on windward shorelines.

Water Temp: Temperature of water at the surface of the pond at the location and time of sample collection. All temperature data provided here is recorded in degrees Fahrenheit.

Status: Summary of monitoring data interpretation intended to provide the public with information to allow informed decision making about recreational pond usage. Note: Lack of information in this category indicates that monitoring has not been conducted at the respective pond. The following five categories are used to describe APCC’s interpretation of monitoring data and are indicated on the map by coloration of lakes and ponds as defined in the legend.

Not Sampled: This pond has not been sampled recently.

No or Low Amount of Cyanobacteria: Results of monitoring indicate no or low amounts of cyanobacteria cells and toxins. Water is clear. This status level suggests that, 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 cyanotoxins. Map color is blue.

Moderate Amount of Cyanobacteria: This status level indicates potential for low to minimal health risks to people but higher potential risks to pets. It is recommended to avoid letting pets interact with the water. This status level is triggered when monitoring data indicate that moderate amounts of cyanobacteria cells and pigments are present. There may or may not be visible particles in the water column or scum on the surface. Cyanotoxin levels are below state guidelines. Map color is yellow.

High Amount of Cyanobacteria: This status level indicates potential for low to moderate health risks to adults but higher potential risks for babies, small children and pets. This status level is triggered when monitoring data indicate that high amounts of cyanobacteria cells and pigments are present. Water clarity is cloudy and significant amounts of suspended particles and/or floating surface scum may be present. Cyanotoxins are likely present but below state guidelines. Map color is orange.

Recreational Use Advisory: This status level indicates moderate to severe health risks for people, children, and pets. This status level is triggered when monitoring data indicate that high levels of cyanobacteria cells and pigments are present. At this public health advisory level suspended particles, surface or shoreline scum is likely to be present, water is likely very cloudy with visibility less than 4-feet, and cyanotoxin levels are at or above state guidelines. Map color is red.

Scum: Indicates presence and type of visible material either as particulates in the water column, as a disperse or dense floating scum on the water surface, or as a scum washed up on the shoreline at waters edge. In order to be classified as scum on this map microscopy has been used to confirm that either type of material is primarily comprised of cyanobacteria cells.

Dominance: Indicates which type (genus) 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.

Cell Count: Number of individual cyanobacteria cells per milliliter (cells/mL) of sample. This data point is often used to determine biomass and associated toxicity and is conventionally used to trigger posting of public advisory notices at ponds.

Phycocyanin: Photosynthetic pigment that is most abundant in common cyanobacteria. Results of pigment analysis using a fluorometer give results for phycocyanin (PC) in micrograms per liter (ug/L), which is a good indicator of total cyanobacteria biomass in a sample. The ratio of PC to CHLA indicates dominance of cyanobacteria over algae and can be tracked throughout the monitoring season to help track growth, indicate community succession events, and predict formation of cyanobacteria blooms.

Chlorophyll-A: Photosynthetic pigment that is most abundant in non-cyanobacterial algae. Results of pigment analysis using a fluorometer give results for chlorophyll-A (CHLA) in micrograms per liter (ug/L), which is a good indicator of total non-cyanobacterial algal biomass. The ratio of PC to CHLA indicates dominance of cyanobacteria over algae and can be tracked throughout the monitoring season to help track growth, indicate community succession events, and predict formation of cyanobacteria blooms.

Microcystin: A potent cyanotoxin that can cause liver damage (hepatoxin) if consumed in high enough quantities. This toxin is produced primarily by a cyanobacteria genus called Microcystis, which is common in ponds across Cape Cod. Analysis of water samples for this toxin is commonly used to manage recreational uses of lakes and ponds and to post or remove public advisory notices. APCC will estimate microcystin levels in water samples using pigment to toxin regressions developed by partner researchers and will confirm higher level samples using toxin test strips and/or lab analysis.

Anatoxin: A potent cyanotoxin that can cause neurological damage (neurotoxin) if consumed in high enough quantities. Little to no monitoring for this toxin has been conducted on Cape Cod to date and there are no local guidelines for safe levels of exposure, yet many of our ponds are dominated by Dolichospermum, which is known to produce this toxin. APCC plans to conduct initial testing for this toxin in ponds with high levels of Dolichospermum to contribute to a baseline understanding of its occurrence on Cape Cod and will update results on the map when available.

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How to use this map:

1. Pan around the map and zoom in/out to locate an area or specific pond you are interested in. You can also search for a location by typing a location or address in the search bar at the top right.
2. 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. For more information about what the results mean, select from the list of terms below for definitions.
3. 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. 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.”

Program Partners


Funding generously provided by:

Mary-Louise & Ruth N. Eddy Foundation, Cape Cod Foundation, Horizon Foundation, Friendship Fund, APCC Members

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 cyano@apcc.org 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