With lakes and rivers already swollen and up to 70 millimetres of rain on the way, Environment Canada has upgraded a previous special weather statement into a rainfall warning Wednesday night.

Toronto could see between 40-70 millimetres of rain between Thursday and Saturday. The alert warns of an increased flood risk for all of southern Ontario.

"The ground, already near saturation, has little ability to absorb further rainfall," it reads.

The heaviest rainfall will happen Thursday and Friday before tapering off to showers over the weekend.

Earlier this week, the Toronto Region Conservation Authority issued a flood watch. Residents of a lakefront Cedar Crest Beach community in Bowmanville continue to use sand bags to protect their homes from rising lake water.