Worcester Firefighters were called to a house at the corner at May and June Street for a report of smoke coming from the structure. Crews arrived and found smoke showing. Once entry was made they found that they had stumbled into a large marijuana grow operation. Firefighters found the structure to have major modifications to it as well as numerous propane cylinders. Police reported finding 900 plants in the house. It was determined there was no fire in the house. Police are investigating.