Blue-Green Algae

Photo courtesy of Public Health Sudbury & Districts.

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 the following symptoms:

  • 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.

Beach Closures

Blue-green algae only pose a risk if swimmers or animals come into contact with it. At unsupervised beaches, you should check the water surface for algae before entering.

The Blue Flag at beaches will be lowered if blooms are present in the swimming area of the main beach. It will be raised again when the algae has moved away.

Warning signs posted at beaches

 Public Health Sudbury & Districts will post caution signs when there has been a confirmed report of a possible bloom near a swimming area. 

Although caution signs stay up for the rest of the summer, this doesn’t mean the water is dangerous. It’s simply a caution to watch for algae before entering the water.

Boating and blue-green algae

Driving your boat through algae blooms breaks up the clumps and can help them dissipate. It can’t be spread to other areas of a lake by sticking to your boat. Although moving your boat from one lake to another will not increase the likelihood of creating blooms elsewhere, washing a boat is always a good practice to help reduce the spread of invasive species, such as Eurasian water milfoil and spiny water fleas.

Blue-green algae and drinking water

Drinking water directly from an affected lake may be unsafe. Municipal drinking water is safe due to extensive purification systems. Treated municipal water is available free of charge at municipal water filling stations.

There is no effective home treatment to remove blue-green toxins from the water. The only safe alternative is to use bottled water or municipal drinking water.

 If you are on a private water system with visible blue-green algae blooms:

  • Avoid using the lake water for drinking, bathing or showering.
  • Avoid cooking with the water - food may absorb toxins from the water during cooking.
  • Do not allow children, pets or livestock to drink or swim in the lake water.
  • Do not boil the water – this may release more toxins into the water.
  • Do not eat the liver, kidneys or other organs of fish caught in the water.

Prevent blue-green algae

Algae will always be present in freshwater lakes. The risk of algae blooms developing can be lowered by reducing or eliminating food sources that stimulate growth. This includes phosphorus and nitrogen in storm water run-off. 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.

Who to contact

Algae blushes and blooms can move in and out of an area within minutes. At supervised beaches, you can speak to lifeguards who are all trained to spot a bloom and advise swimmers accordingly.

It is best to be cautious. 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 and Climate Change at 705-564-3218 during regular business hours.