Provincial police have arrested 45 people and laid 173 charges in connection with an outdoor marijuana grow-operation near Minden last fall.

After six passersby stumbled upon the grow-op near an ATV trail last October, they were beaten, robbed and held captive for hours by the suspects, police said.

"They were accosted at gunpoint ... one individual was shot at," OPP Det. Insp. Ken Leppert said at a news conference on Tuesday.

"All of these six victims were forcibly confined in one way or another for several hours and robbed of their identification and cellular phones."

The victims, two of whom were Ministry of Natural Resources contract employees, managed to escape after being held for about three hours.

Police said marijuana plants were being stolen from the spot by another group of criminals when the victims discovered the plants.

"Criminals stealing from criminals or drug traffickers stealing from drug traffickers is concerning because they not only have to guard themselves against the police, but now they're arming themselves against one another," Leppert said.

Officers have seized more than $7 million in marijuana, about $50,000 in cash, 2,000 ecstasy pills, nine firearms and camouflage outfits.

The investigation, dubbed Project Pirate, also resulted in charges against several people in connection with a violent carjacking last June. In that incident, a man was carjacked and then shot on Highway 401 near Belleville.

Investigators say there could be more arrests in their probe.

Police say there could be more than 300 illegal outdoor marijuana grow-ops right now in Ontario, some in remote areas and others hidden in farmer's fields.

Residents who are out camping and hiking are being warned that coming across these fields can be dangerous.

"If you were to come across one, the smart thing to do is to leave the area forthwith and contact the police department in the area, and in rural Ontario that would be the OPP," said Det. Insp. Brian Martin.

With a report from CTV Toronto's John Musselman