Toronto Hydro doesn't know if it was the squirrel or a piece of defective equipment that caused a short in the system.
A dead squirrel, apparently electrocuted, was found in the substation at Wellington and John Sts. this morning.
The area west of Yonge St. to Spadina Ave. and from Queen St. south to the lake was affected.
Some businesses and residents lost power and some traffic problems were reported. The power was disrupted for just under two hours.
"Aside from storms, animal contacts do cause a lot of outages," Toronto Hydro spokesperson Tanya Bruckmueller said. "Less in the downtown area," she added. "It's more common on overhead lines in the suburban areas."