Hamilton Public Health officials have detected toxins in the algae growing across the city’s shoreline and have issued a warning — avoid touching the cloudy green water, keep pets away and don’t eat fish caught in these areas.  

"There’s toxin present but it’s not at high, high levels that will cause health effects," said Matt Lawson, the city’s manager of environmental health. "We thought it was prudent to advise residents of it."

Exposure to high levels of cyanobacteria-contaminated water can cause a range of symptoms, including skin irritation and itching, headaches, fever, diarrhea, abdominal pain, nausea or vomiting.   


Blue-green algae seen around Bayfront Park. (Kate Adach)

Blue-green algae — known as cyanobacteria — coats much of the lake’s surface near Bayfront Park and the western Hamilton Harbour, where water appears green and hazy.  

This is a common seasonal problem, Lawson said. But the city’s recent high temperatures may have spurred the algae growth about three weeks early.  

Hamilton resident Jeremy Biehn has been fishing around the city for years. He says the current water conditions are the worst he’s ever seen.  

"It’s abnormal this season," he said. "You throw many casts out there and they come back full of weeds."  

Biehn, who wasn’t deterred from fishing with his fiancé and three-year-old son this week, said he feels confident the "bad season" is due to too much hot weather.   

The algae is also a problem for the Bay Area Restoration Council, which has been working to clean the city’s waterfront. Hamilton Harbour has remained an "area of concern" in the Great Lakes Water Quality Agreement since the 1980s.  

"Despite all of the improvements we’ve seen over the decades, this kind of algae growth is a big concern," said Chris McLaughlin, executive director of the council.  

McLaughlin said the council will not be able to delist the harbour as an area of concern if phosphorus and blue-green algae levels remain high. 

But toxicity levels are not detectable by the naked eye, Lawson said. That’s why the city tests the water four times a week and has posted signs along the shoreline warning people of the current conditions.  

Rather than attempting to judge the water by its appearance, residents are advised to refer to the signage posted around the shoreline.