Is it safe to swim in Lake Ontario? - Metro US

Is it safe to swim in Lake Ontario?

“You can check the water quality at any of the GTA beaches at


or call the hotline at 416-392-7161.”“You can check the water quality at any of the GTA beaches at
or call the hotline at 416-392-7161.”

Aaah, summer. When a person’s thoughts turn to swimming.

There are many options for swimming: Municipal pools, private pools, trips to Wasaga Beach and, of course, the big blue puddle we live beside, Lake Ontario. The GTA has several beaches on Lake Ontario that are open to the public. Is it safe to swim there though? Isn’t it polluted?

The GTA beaches are tested daily by the Toronto Department of Works and Emergency Services. They test for E. coli, a species of bacteria present in our intestines. When ingested in large numbers, these bacteria can cause upset stomachs ranging from mild to extremely severe. Some, albeit rare, strains of E. coli can be fatal.

E. coli is actually used as an indicator organism, however. Since E. coli lives in the intestines of humans and other animals, it is excreted with fecal material and its presence is an indication that fecal material has entered the water. This fecal material may contain other pathogens that can cause stomach upset, diarrhea, skin rashes and infections of the ear, nose and throat.

How does this material get into the water? Most of the problem is due to the storm sewer system. The storm sewer system collects rainwater that runs off roads and yards into the grates we see along roadsides. This water is released untreated into the lake. If the rainwater washes animal feces into the lake, this can cause contamination, therefore, large amounts of unscooped doggy droppings can lead to measurable levels of E. coli.

Pesticides and fertilizers sprayed onto lawns are often washed into the storm sewers by the rain and these impact the water quality at our beaches, as well.

Alongside the storm sewer system is the sanitary sewer system. It is this system to which our household drains, toilets, etc., are hooked. This wastewater does get treated before being released. Some sanitary drains are accidentally or illegally hooked into the storm sewage system instead of the sanitary system, and this means raw human waste can be released into the lake.

The third way for pathogens to get into the lake is through accidental releases. In some older parts of the city, the storm sewer and sanitary sewer systems are the same system. When it rains heavily, the sewage treatment facilities cannot cope with the increased volume, and raw sewage ends up being released into the lake. Mercifully, the city is working to separate the two sewage systems, and this type of release is becoming rarer.

The bottom line — is it safe to swim in our lake?

The answer is often yes. You can check the water quality at any of the GTA beaches at www.torontobeach.caor call the hotline at 416-392-7161. These sources will tell you the E. coli count at the beaches. Beaches are usually closed when the E. coli count is greater than 100 counts per 100 ml of water. At this level, it is considered pathogens may be present at high enough concentrations to cause illness.

I would suggest, as much as possible, keep your eyes and mouth closed in the water, but, conditions permitting, don’t deny yourself the opportunity to cool off in “Our Lake.”

Andrew Laursen is an assistant professor in the department of chemistry and biology at Ryerson University and is a member of the environmental applied science and management program in graduate studies. His research is in the area of ecosystem ecology. Sophia Dore is an environmental scientist with Conestoga-Rovers & Associates, an environmental consulting company. Contact Andrew Laursen at earthtones.metro@gmail.com

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