WATERLOO, Ont. - Thunderstorms and high winds have left a swath of damage in southwestern Ontario.

Five people were injured at the farmers' market in the St. Jacobs area near Waterloo when winds knocked down several tents Saturday.

Environment Canada says it will send an investigator today to determine whether it was high winds or a tornado that was to blame.

Waterloo regional police say there was a lot of damage in Heidelberg where the winds downed trees and hydro lines.

Tree branches were also knocked down and a tree fell onto the road at Portage and McLeod in Niagara Falls.

More than 5,000 home and businesses in Pelham and Wainfleet lost power for several hours Saturday because and Grimsby got hit with heavy rain, high winds and hail.