News Releases

Frequently Asked Questions - Lake Erie Algal Blooms

Tuesday, Jul. 17, 2012

What are blue-green algae?

Blue-green algae are primitive, microscopic plants that live in fresh water. Their scientific name is Cyanobacteria but they are commonly known as 'pond scum'. Normally blue-green algae are barely visible. These algae thrive in areas where the water is shallow, slow moving, and warm, but they may also be present below the surface in deeper, cooler water.

What are algal blooms and why do they happen?

When certain conditions are present, such as warm weather, low winds and high levels of plant nutrients in the water, blue-green algae populations can very quickly increase to form a large mass called an algal bloom. The bloom can cause the water to have a foul odor and pea-soup colored foam, scum or mat appearance. Algal blooms can block sunlight that other organisms need to live. When the algal blooms start to die, the oxygen in the water starts to deplete. Blooms most commonly occur during the late summer and early fall.

The main plant nutrients that help plants grow are phosphorus and nitrogen. These substances are present in household and agricultural fertilizers, wastewater from industries, waste management systems and septic systems. Plant nutrients are carried to water bodies through rain runoff or when snow melts, and become a source of food for algae and other plants. Phosphorus greatly influences the growth of algal blooms.

Are algal blooms poisonous?

Some algal blooms can produce toxins that are harmful to the health of people, animals, plants and the environment. The most common toxins in blue-green algal blooms are called microcystins. These toxins are released to the water when the algae cell wall is broken. As a precaution, any blue-green algal bloom should be regarded as being potentially toxic.

Different blue-green algae toxins can irritate the skin or cause damage to the liver or nervous system. If you drink water or eat fish or blue-green algal products (such as health supplements) containing elevated levels of toxins, you may experience headaches, fever, diarrhoea, abdominal pain, nausea and vomiting. If you swim in contaminated water, you may get itchy and irritated eyes and skin, as well as other hay fever-like allergic reactions. Children are at greater risk than adults of developing serious liver damage if they swallow high levels of toxins, because of their comparatively lower body weight. Pets and other animals could also become extremely ill and even die due to liver or nervous system damage. If you suspect you might have come into contact with blue-green algae toxins and are experiencing any of the above symptoms, rinse any scum off your body and consult your physician immediately.

What happens if blue-green algae is present in my drinking water?

Municipal drinking water systems test for a common blue-green algae toxin at least once a week when blue-green algae is observed at or around the water intakes. The test is done on both raw source water (untreated) and treated water. If the toxin is found to be at levels higher than the respective treated water standard, the Ministry of Environment (MOE) is notified. MOE in turn notifies the local Health Units, municipalities, Conservation Authorities and other stakeholders. Local Health Units notify the public.

Who do I call if I suspect the bloom is blue-green algae?

If you suspect a blue-green algae bloom, assume toxins are present. Avoid using the water for any purpose and call the Ministry of the Environment (MOE) Spills Action Centre (SAC) at the phone number: 1-800-268-6060.

What do I do if I see blue-green algae on my shoreline?

  • Avoid all contact with the water
  • Use alternate water sources as needed
  • Keep children and pets away from the algae
  • Do not use the water for drinking or any other purpose; note that countertop jug filtration systems do not properly remove the algae from water
  • Do not boil the water as this may release more toxins
  • Do not add any chemicals to the water, as the use of herbicides, copper sulfate, other algaecides and disinfectants like chlorine may also release more toxins

How can blue-green algae be reduced or prevented?

Algae needs plant nutrients to grow. Reducing or eliminating the plant nutrient input to water bodies is key to reducing or preventing the growth of blue-green algae. Urban and rural best management practices such as using phosphate-free detergents, eliminating the use of fertilizers and maintaining naturalized shoreline on lakefront properties, proper maintenance of septic tanks and reducing agricultural runoff (for example, through crop rotation and cover crops) will all help reduce the nutrient input to water bodies.

What other testing for blue-green algae toxins in Lake Erie is being done?

  • This year (2012), the Ministry of Environment is undertaking sampling in the western basin of Lake Erie and in the Lake St. Clair during the summer-fall months to test for the blue-green algae toxin, microcystins, in the nearshore waters. Test results will be shared with local Conservation Authorities and other organizations. You can call Chitra Gowda, Water Quality Specialist, Essex Region Conservation Authority, at 519-776-5209 ext. 342 for more information, and go to the website below to view the results:
  • The National Oceanic and Atmospheric Administration (NOAA) Center of Excellence for Great Lakes and Human Health located in Ann Arbor, Michigan, tests for microcystins weekly during warmer months as well, at several locations in the western basin of Lake Erie. Microcystins data from 2011 and previous years may be viewed at:

  • A Harmful Algal Bloom (HAB) Bulletin has been developed by NOAA to provide a weekly forecast for toxic algal blooms in western Lake Erie. When a harmful bloom is detected by the experimental system, scientists will issue the forecast bulletin. The bulletin depicts the HABs' current location and future movement, as well as categorizes its intensity on a weekly basis. The bulletin is available at:

Sources of information:

  • Ministry of Environment

  • Environment Canada

  • Health Canada

  • Centers for Disease Control and Prevention

  • National Oceanic and Atmospheric Administration (NOAA) Center of Excellence for Great Lakes and Human Health