Emergency crews discovered a large indoor marijuana growing operation while responding to a barn fire on Clarke McKinlay Rd. in Hamilton Township Saturday afternoon. Firefighters arrived on scene at about 2 p.m. and found heavy smoke coming from the east side of the barn. The fire was too involved to send crews inside, so firefighters attacked the flames from the perimeter. An investigator with the OPP's Street Crime Unit says emergency responders found a large number of marijuana plants inside the barn. The investigator says the number of plants exceeds the legal requirements for growing cannabis. The Ontario Fire Marshal's Office is investigating the cause of the blaze and the OPP says it will execute a search warrant on the property once that investigation is complete.