Five of Toronto's supervised public beaches were marked unsafe due to E. coli bacteria levels on Saturday and one expert says water contamination will likely get worse because of rainstorms.
Toronto Public Health analyzes water samples from the city's swimming beaches daily from early June to Labour Day. E. Coli counts of more than 100 Colony Forming Units (CFUs) per 100 millilitres of water at a particular beach means people should not swim there.
According to the city, the beaches currently deemed unsafe are Sunnyside Beach, Hanlan's Point Beach, Gibraltar Point Beach, Centre Island Beach and Ward Island's Beach.
Five other beaches currently deemed safe, meanwhile, are Marie Curtis Park East Beach, Cherry Beach, Woodbine Beaches, Kew Balmy Beach and Bluffer's Park Beach.
James Li, a civil engineering professor at Ryerson University in Toronto, said on Saturday that the key is to manage water pollution related to storms. That can be done by governments heavily investing in infrastructure, such as sewage treatment plants, and also by taking steps to reduce runoff into the water.
It's all about lessening the impact of storms on water quality, he said.
"The best way to reduce water pollution from storms is to let it infiltrate back to the soil so that we don't deal with it at the end when it reaches the river," Li told CBC Toronto.
According to Mahesh Patel, manager of health environments for Toronto Public Health, high E.coli counts can make swimmer sick.
"Swimming in water with E.coli levels greater than the City's standard exposes the bather to increased risk of infections, including ear, eye, nose, throat and skin infections. If beach water is ingested, it may cause upset stomach, vomiting or diarrhea," Patel said in an email.
If beaches are considered unsafe for swimming, Toronto Public Health will post the information on its website, through its beach water quality hotline at (416) 392-7161 and through signs posted at the beach.
Heavy rainfall can cause bacteria levels to rise at beaches
Bacteria levels can rise in the water at Toronto's beaches for the following reasons: recent heavy rainfall; large number of birds; large number of swimmers in the water; strong wind and high waves; and cloudy water.
It usually takes up to 48 hours following the weather and other conditions before E.coli levels may decrease and fall below the 100 E.coli/100 ml of water threshold.
Patel said Sunnyside and Marie Curtis Beaches are affected by the Humber River and Etobicoke Creek, respectively, and Cherry Beach may be impacted by flow from the Don River to some extent.
"Rainfall anywhere on the watershed will bring contaminates into Lake Ontario," Patel said.
"As there have been several days over the past week with heavy rainfall, we anticipate that E. coli levels will remain high at several beaches, including some that have been already posted as unsafe for swimming, particularly those with other water inputs due to runoff."
According to the city, lifeguards fly large coloured flags at Toronto's swimming beaches to notify the public of the water conditions.
When its beaches meet high standards for water quality, safety, environmental management and education, lifeguards fly the blue flag.
Red flags indicate high hazard conditions, including extreme wave action and/or currents and/or E.coli counts over 100 Colony Forming Units (CFU) per 100 millilitres and people should not swim there, the city said.
Green flags indicate low hazard conditions that are good for all swimmers. Yellow flags indicate moderate hazards are present including rough water, and strong off-shore winds and only strong, experienced swimmers should consider swimming.