(blue-green algae)

Cyanobacteria (blue-green algae) are a natural and essential part of our environment and water ecosystems, and can be found in many ponds, lakes, rivers, and wetlands in New Brunswick. Not all cyanobacteria are harmful, but some can produce toxins, which can impact the health of humans and animals.

Get to know cyanobacteria

Cyanobacteria is the proper name for blue-green algae, because these organisms are actually bacteria and not algae at all! Cyanobacteria were the earliest known forms of life on earth. When first discovered, cyanobacteria looked similar to algae and can sometimes appear blue-green in colour – which is why the term blue-green algae was used. 

They are a natural part of our environment and water ecosystems, and can be found in many ponds, lakes, rivers, and wetlands in New Brunswick. Blooms usually occur when temperatures get warmer, typically in the late spring and early summer sometimes appearing quickly or overnight. They are not normally visible, but under certain conditions (warm, slow moving, shallow water and lots of sunlight) and when there is lots of food (nutrients such as phosphorus and nitrogen), they can grow quickly and clump together to form surface blooms or benthic mats.

Some types of cyanobacteria can produce toxins that are harmful to humans and animals. Because of this, public health advisories may be issued.  Advisories help recreational water users make informed decisions on water use in the affected area. They also help remind users to check the water for visible surface blooms, scum, and benthic mats, which pose the most risk.  Since conditions may change in a matter of hours, it is important to be aware of local water conditions.  Individuals should always check the water and scan the shoreline before engaging in recreational water activities such as swimming, wading, canoeing and paddle boarding, etc.  Avoid swimming in areas with visible surface blooms or benthic mats.


Types of cyanobacteria blooms

In New Brunswick, there are two types of cyanobacteria blooms to look out for:

Surface blooms

When there is lots of food (nutrients such as phosphorus and nitrogen) in the water, cyanobacteria can grow very quickly and clump together to form a surface bloom. A surface bloom will look like surface scum, foam or mat and often be blue-green in colour. Surface blooms can also look red, brown, or green. Some surface blooms look like paint streaks on the water, while others may not affect the look of the water.  Fresh surface blooms can smell like newly mown grass while older blooms can have a foul smell, sometimes like garbage.

Surface blooms usually occur when it begins to get hot outside, typically in the late spring and early summer.

Cyanobacteria surface blooms can appear quickly or overnight. On windy days cyanobacteria blooms may accumulate near the shore.

Surface blooms can also be suspended at different depths in the water. This can make them more difficult to see. They can float up and down in the water and move to where there is more food (nutrients) and light. So even if a surface bloom is not floating on the surface of the water, it doesn't mean that one isn’t present.

While not all cyanobacteria blooms are harmful to human health, some can produce toxins. The most commonly found toxin in North America is microcystin, which can cause skin, eye and throat irritations and more severe illness if consumed.

Benthic mats

Benthic mats are a natural and essential part of our freshwater ecosystem that grow on the bottom of rivers and lakes. These mats can grow quickly when the water is warm, there are stable flows and lots of food (nutrients).  Benthic mats look like clumps of vegetation, and can appear black, brown or dark green in the water.  On the shoreline they may appear brown or grey once they have dried. Animals can be attracted to their odour.  The mats can contain a mixture of algae and cyanobacteria.  

Benthic mats can break away from the bottom of a lake or river and wash up along the shoreline, making them accessible to pets and children. They can also be attached to rocks or aquatic plants or may be found floating in the water or along the surface.

Children should not play with the mats, and pets should be kept away from algal mats or plants that are found floating near the shore or that may have washed up along the shoreline.

Dogs can be attracted to the odour of benthic mats and may want to eat them. Dogs should not eat vegetation or floating mats found along the shores of lakes or rivers as they may be lethal.

Be informed and stay safe

Cyanobacteria can produce toxins, which may cause skin, eye and throat irritations. More serious health effects such as gastrointestinal illness can occur if toxins are consumed.

Being active and enjoying the outdoors has many benefits for your physical and mental well-being.  Public Health New Brunswick encourages you to be active and enjoy the outdoors, but to be alert and take precautions.  There are always things you can do to protect yourself while enjoying recreational waters.

Public Health New Brunswick recommends the following safety advice:

  • Always supervise children and pets near recreational water.  They may be more at risk of becoming ill.
  • Always check the water and avoid swimming in areas where there are visible surface blooms, scum or benthic mats are present.
  • Do not enter the water with open cuts or wounds.
  • Always wash your hands before eating.
  • Do not use water from areas with cyanobacteria blooms for washing, drinking or cooking. Boiling the water will not remove toxins. Always obtain drinking water from a clean and safe source.
  • Fish caught from water where cyanobacteria blooms are present should have all their organs removed and be rinsed well with clean drinking water before being cooked and eaten.
  • Even if no cyanobacteria blooms are present, it is recommended you shower with clean water after being in recreational waters.

Toxins can sometimes remain in the water for several weeks after surface blooms are no longer visible. As a precaution, it is recommended that recreational water use be avoided in areas where surface blooms are present.

If you begin experiencing symptoms or health effects you should seek medical advice from a health-care provider.

Protecting your pets

Why are cyanobacteria (blue-green algae) dangerous for dogs and other animals?

Some cyanobacteria produce toxins that could be harmful to a dog’s liver and brain. Dogs are attracted to the odour, and if ingested, they may:

  • Vomit and be sick
  • Have a seizure
  • Experience breathing difficulties
  • Have diarrhea
  • Collapse and become unconscious
  • Die

Call a veterinarian right away if you suspect cyanobacteria poisoning.

How can I avoid cyanobacteria?

  • Always check the water and shoreline for blooms and mats.
  • Do not let dogs drink or swim in water where visible blooms or mats are present.
  • Do not let dogs eat benthic mats or vegetation floating in the water or along the shore.
  • On hot days, consider walking your dog in the morning or evening.
  • Always take fresh water on walks for you and your dog.

Report a suspected cyanobacteria bloom

The Department of Environment and Local Government plays a part in the management and protection of New Brunswick waters. It has developed a protocol to consistently address occurrences of cyanobacteria blooms.   If you encounter what you suspect might be a cyanobacteria bloom, please report it by calling the appropriate Department of Environment and Local Government Regional Office.

In order to assist department staff in addressing your concerns, it would be helpful for you to provide the following information:

  • The name and location of the affected body of water.
  • The type of body of water (lake, stream or pond).
  • Colour of the bloom or mat?  Photos would be helpful, if possible.
  • Is there a yellow scum on the surface of the water (this would likely be pollen deposition)?
  • Is the bloom only on the surface or does the bloom seem to be distributed throughout the water column?
  • Does the bloom seem to only occur along the shoreline?
  • The length of time the issue has been occurring.
  • Any additional information or observations.

Cyanobacteria advisories

Once an advisory is posted, it will remain on the list indefinitely. Although each summer the area of water indicated may not have cyanobacteria blooms, they are left on the list for visitors to be aware that they could possibly recur since the area has had cyanobacteria blooms in the past. Future sampling of the area will not be undertaken to rescind any advisories due to the unpredictability of cyanobacteria blooms.

Public Health New Brunswick encourages the public to be active and enjoy the outdoors but be aware that cyanobacteria blooms can be unpredictable. Advisories help local recreational water users make informed decisions on water use in the affected area. We encourage everyone to be more aware of the formation of highly visible surface blooms and scum; and benthic mats that have washed up on shore, which pose the most risk.

In addition to advisories posted on this website, health advisory signage will be installed indicating that blooms have been observed at the affected body of water.

Preventing cyanobacteria

Although nutrients are naturally occurring in bodies of water and are needed for plant and animal life, too much phosphorus and nitrogen can cause problems by offsetting the natural balance of the lake.  These problems arise or are compounded when storm water, agricultural runoff, industrial and wastewater effluent, faulty septic systems and lawn fertilizers find their way into the body of waterbodies.

We can all play a key role in the prevention of cyanobacteria blooms by helping to keep excess nutrients from entering the water. Homeowners can:

  • Maintain a buffer of natural vegetation (trees, shrubs) along waterbodies to help filter run-off and provide shade to keep the water temperature cool.
  • Avoid the use of fertilizers and herbicides near water.
  • Use phosphate-free cleaning products.
  • Maintain your septic system and locate it far from the shore.



The Government of New Brunswick (GNB) supports various cyanobacteria research projects through the Environmental Trust Fund. These research projects are taking place within the Saint John River as well as in lakes across the province. The projects will help us to better understand the distribution of cyanobacteria and their toxins in our recreational waters.

These research projects use various methods or tools to assess whether cyanobacteria and/or their toxins are present in the water. These methods/ tools include:

  • Identification of cyanobacteria and counting of cyanobacteria cells using microscopes.
  • Testing water for toxins, such as microcystins.
  • Testing the water for the presence of cyanobacteria genes responsible for producing the certain cyanobacteria toxins. The presence of the gene (a unit of DNA) responsible for producing toxins may or may not mean that toxins are present.



Health Canada: Guidelines for Canadian Recreational Water Quality

Guidance on the factors that can interfere with the safety of recreational waters from a human health perspective.

Environment Canada: Water and Environment

Water quantity, freshwater quality, cleaning up our lakes and rivers, water science, sustainability indicators, marine water quality, protecting water.

ACAP Saint John: Cyanobacteria and cyanotoxins

ACAP Saint John is leading a partnership of organizations in advancing research, cyanotoxin monitoring, and education in the lower Wolastoq/Saint-Jean/Saint John River.

Educational signage

Beginning in 2022, GNB is working with key partners to install educational signage at recreational bodies of water throughout New Brunswick.  These signs do not necessarily indicate cyanobacteria blooms have been observed in the bodies of water.  The purpose of these signs is to educate the public on the different type of blooms in New Brunswick, display picture to help identify cyanobacteria blooms and to share precautionary information to help the public stay safe while enjoying recreational water activities.




Green Home and Cottage (PDF)

A quick reference guide to ‘green living’ for shoreline property owners