Smoke from forest fires in northern Quebec triggered a smog advisory in Ottawa and across much of eastern Ontario.
The smog advisory was issued Tuesday by Environment Canada and the Ontario Ministry of the Environment.
People are encouraged to take public transit or carpool to help reduce smog.
The major contributor to the poor air quality are the forest fires near James Bay, about 700 kilometres away.
The smoke is being pushed by winds toward Ottawa and as far south as Kingston.
"They are quite large fires, because they are in an area where we do not intervene," said Melanie Morin of Quebec's forest fire prevention agency.
The fires are under surveillance, she said, adding that the winds are shifting and the air in Ottawa should start improving Wednesday.
In the meantime, Ottawa Public Health is asking for co-operation from the public.
Environment Canada is advising people to not use gas-powered motors, aerosol sprays and solvents.
The smoke is expected to clear by Wednesday evening.