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Blue-green algae found in Lake Ontario

No sign of blooms, which can cause problems for both humans and animals

On July 30, the Durham Region Health Department advised it had been notified of the presence of blue-green algae in water samples taken from Paradise Beach in Ajax. To date, there have been no algae blooms detected, which can be harmful to human health. (Photo by Joel Wittnebel)

By Dave Flaherty/The Oshawa Express

Blue-green algae have arrived in Lake Ontario, but so far the waters surrounding Oshawa are clear.

On July 30, the Durham Region Health Department advised it had been notified of the presence of the algae in water samples taken from Paradise Beach in Ajax.

However, the amount detected does not indicate a bloom in the water.

According to Craig McIlmoyle, a senior public health inspector, the true concern starts when these blooms appear.

Blue-green algae are microscopic, plant-like organisms that occur in ponds, rivers, streams, and lakes.

Although called blue-green algae, they can also be olive-green or red.

The algae are not usually visible in the water but become more clear when the large mass or scum called blooms begin to develop.

Blooms typically occur around this time of year and thrive in areas where the water is shallow, slow-moving and warm, but may be present in deeper, cooler water.

According to McIlmoyle, a contributing factor to the development of blooms is an overabundance of nutrients like phosphorus or nitrogen.

McIlmoyle says just because the algae have appeared in the Ajax area doesn’t necessarily mean it’s coming farther east.

“I would say no. I think that these blooms are very localized. It really depends on the water conditions,” he says.

In fact, according to McIlmoyle, this is the first time blue-green algae is confirmed on the shores of Lake Ontario in Durham.

“It’s indicative of a changing environment and as temperatures get warmer we are starting to see it more,” he says, adding the public has become increasingly aware of the problem in recent years.

Blue-green algae can pose a threat to both humans and animals. Potential effects range from irritated eyes, headaches, fever, diarrhea, abdominal pain, nausea, and vomiting.

Exposure to larger quantities can result in more serious health effects such as liver damage.

McIlmoyle says when it comes to the bacteria, caution is always the most effective practice.

“If members of the public go to a beach and they observe what they believe is blue-green algae, the best advice is to avoid it,” he says.

He also advises they contact the Durham Region Health Department’s Environmental Help Line at 905-723-3818 or 1-888-777-9613.

When blue-green algae blooms are apparent, residents should assume toxins are present, do not use the water for cooking, bathing, drinking or swimming, and restrict pet and livestock access to the water.

If the bloom is near a water supply, keep in mind that home treatment systems may not remove toxins and can get overwhelmed or clogged.

Treating affected water with chlorine or other disinfectants can potentially increase the toxin levels.


Here are some tips to help minimize the possibility of blue-green algae:

  • Use phosphate-free soaps, detergents and cleaning products
  • Avoid using lawn fertilizers, especially those that contain phosphorus
  • Ensure your septic tank is in good working condition and not leaking into the water
  • Clean up after your pets
  • Maintain a natural shoreline on waterfront properties
  • Plant and maintain native vegetation along waterways to reduce agricultural runoff