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Blue-Green Algae

Closing Nepahwin Beach Since 2015

Nepahwin Lake has had late summer blue-green algae blooms annually in 2015 to 2018 inclusive. The City of Greater Sudbury website provides the following information about blue-green algae.

Blue-green algae are organisms that live in freshwater lakes around the world. Normally, they are barely visible but, under certain conditions, they can multiply to form a large mass called a bloom or a blush.

Most blooms or blushes contain plant species that are harmless; however, the presence of even one toxic species can pose a risk. Only laboratory tests can determine whether a bloom is toxic.

Causes of Blue-Green Algae
  • Blue-green algae blooms are well suited to lakes with high phosphorus and nitrogen levels.

  • Warming water temperatures can cause more frequent algae blooms.

  • Spreading of road salt does not cause blue-green algae blooms.


Recognizing Blue-Green Algae
  • Blooms usually look like bluish-green pea soup but can also be olive-green or red.

  • When the bloom is very large, algae may form solid-looking clumps floating on or just below the surface of the water.

  • Fresh blooms often smell like newly mown grass. Older blooms smell like rotting garbage.


Symptoms From Contact

Contact with toxins released from certain species of blue-green algae can result in: 

  • itchy, irritated eyes and skin

  • headaches, fever, diarrhea, abdominal pain, nausea and vomiting if you swallow contaminated water

  • more serious health effects if contaminated water is consumed in large quantities.

Animals should be kept away from surface water sources during a bloom. Symptoms may range from lethargy and loss of appetite to seizures, vomiting and convulsions.


Who to contact if you suspect a blue green algae bloom:

At supervised beaches, you can speak to lifeguards who are all trained to spot a bloom and advise swimmers accordingly.

If you suspect a blue-green algae bloom, assume toxins are present. Avoid using the water and contact Public Health Sudbury & Districts at 705-522-9200 or the Ministry of the Environment, Conservation and Parks at 705-564-3218 during regular business hours.


How residents can help reduce the chance of blue green algae blooms:

Read more about green gardening and lawn care practices and follow the City’s lawn fertilizer by-law to help control blue-green algae blooms.



Public Health Sudbury and Districts:

City of Greater Sudbury:

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