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Algae Blooms and Cyanobacteria in New Brunswick

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Surface blooms

  1. 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.

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

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

  4. 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.

  5. 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

  1. 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.  

  2. 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.

  3. 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.

  4. 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.

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