Environment Canada has ended a special air quality statement that warned of thick smog.
A thick, concentrated haze was expected to blanket the Toronto area as hot, humid temperatures mingle with air pollution.
The combination of heat, sun and light southerly winds was expected to cause "increasing ground-level concentrations" in Toronto and the Halton-Peel and York-Durham regions.
"Individuals may experience symptoms such as increased coughing, throat irritation, headaches or shortness of breath," the statement said.
Children, seniors and those with cardiovascular or lung diseases are particularly at risk.
