It's already infamous for drowning a Ferrari, and now city officials are warning the Lower Simcoe Street underpass could flood again during the rain storm heading Toronto's way.

The street's storm sewer pipes are built lower than most in the downtown area, which makes them vulnerable to filling with water from Lake Ontario, which is currently sitting at the highest level it's been in decades.

With between 40 and 70 millimetres of rain expected to fall by Saturday, there's a major risk of flooding. Crews are ready to pump the water out if that happens, but the city's still urging motorists to consider other routes.

"In the event that we do get the forecasted rain that's being called for, motorists are best to avoid that area," said city spokesperson Wynna Brown.

Early Thursday afternoon, as the rain started to fall, water was already rushing into the storm drain in the street's southbound bike lane.

Toronto Water crews have been working to stormproof the underpass, but the roadway will require major work before it can handle severe storms. (John Rieti/CBC)

Lower Simcoe has been the site of flooding throughout the spring months, which is causing the city to consider changes in the future. Workers are currently rebuilding part of the storm sewer in the area, which a Toronto Water spokesperson says is the first phase of a more permanent repair to the roadway.

That work is expected to cost less than $100,000.

Toronto Water also has a plan, currently in the review and design stage, for changes that will include the addition of a new storm pump.

The city is warning drivers to keep an eye out for pedestrians during the rain storm. (John Rieti/CBC)

Brown also urged motorists to take extra caution during heavy rain and keep an eye out for pedestrians and cyclists.

Toronto has already received more than 100 millimetres of rain since the beginning of April, according to the city, leaving much of the ground completely saturated. That could add to the amount of water flowing onto local roads and cause flash flooding in some areas.

"All parts of Toronto can be affected by flooding and there may be little or no advance warning that localized flooding is imminent," the city warned in a Thursday news release.

Anyone who spots serious flooding should call 3-1-1.