Heavy snowfall and poor visibility led to a 20-car crash on Monday afternoon outside Waubaushene.
Southern Georgian Bay OPP were forced to shut down southbound lanes on Highway 400 north of Coldwater at 2:45 p.m.
Provincial Const. David Hobson said the crash was weather related.
A reporting centre was set up at the fire hall in Waubaushene as emergency services dealt with the aftermath of the multi-car pileup.
Hobson noted several people involved in the crash were treated for minor injuries.
The highway was reopened at 5:15 p.m.