As of today, the city has 46 human cases this summer, Toronto Public Health said.
The city expects more cases in the coming weeks.
In comparison, in 2002, the city had 163 reported cases. The following year there were 44 cases. Some years there has been none.
"While most people infected with West Nile Virus will recover, the virus can have serious health impacts — especially for seniors and those with compromised immune systems," said Dr. David McKeown, Toronto's Medical Officer of Health.
"I urge everyone to take precautions to avoid being infected with the virus," he added in a release.
The city is setting mosquito traps for weekly testing and larviciding catch basins to reduce mosquito populations.
Public health authorities recommend wearing Health Canada-approved mosquito repellent and covering up or going indoors when mosquitoes are most active at dusk and dawn.
They also advise making sure that door and window screens fit tightly and have no holes that may allow mosquitoes inside.
Quebec, Alberta, Manitoba and Saskatchewan have also reported human cases this year, but in low numbers.