York Regional Police say the incident took place on the evening of July 2 at the Strawberry Festival in Whitchurch-Stouffville, Ont.
They say multiple people called to report that pepper spray, bear repellant or a stink bomb had been released into a tent that held about 700 people.
Police say witnesses believe a group of teenagers may have been responsible, but no suspects have been identified at this time.
Investigators are asking anyone with photos or video of the incident or information about what happened to contact them.
They say it’s still unclear what the substance was, but its effects were temporary and no long-term problems have been reported.
