More than 10,000 customers were affected across the GTA, Guelph, Waterloo Region and Wellington County.
Power was cut to several schools in the area, including the University of Waterloo, which sent students home early from classes. Wilfred Laurier University and several highschools were also in the dark.
Several accidents were also reported at intersections where lights were out.
Hydro One restored power by 6 pm.