AUBURN – A man unloading a truck full of watermelons for the Good Shepherd Food-Bank on Thursday stumbled upon a different crop: a hefty load of marijuana.

The volunteer at the Hotel Road warehouse said he was picking through the watermelons when he spied the large bale near the front of the tractor-trailer.

“We didn’t know what it was, so I put it outside,” the man said.

The bale, wrapped neatly in packing tape, later proved to be 20 pounds of marijuana. It was believed the pot came all the way from Mexico.

“It’s definitely bizarre,” said the man, who did not want to be identified.

Soon after the bale was discovered, police were called, and drug agents were sent to the food bank. An agent quizzed the man who had unloaded the bale but quickly determined he had nothing to do with the illegal shipment.

“He asked me, How long have you known the watermelon man?’ I told him, I didn’t know him at all,” the volunteer said.

The street value of the marijuana shipment was likely about $20,000, according to a local police office who formerly was a narcotics agent.

Investigators from the Maine Drug Enforcement Agency said the watermelons and illicit pot originated in Mexico. The shipment went to the Boston area, where a trucking company picked it up.

Good Shepherd, which channels food to a network of food banks throughout New England, received the shipment Thursday afternoon. For all the trouble the cargo caused, the watermelons were not even that good.

“A lot of them were all smashed,” the volunteer said.

By the time a drug agent began snooping around, the truck driver was gone. Investigators were looking for the man in the Boston area Thursday night, but they do not believe he had anything to do with the marijuana, either.

Most likely, a drug trafficker south of the border loaded the pot and either forgot about it or was forced to abandon the shipment, investigators said. The original source of the pot is not expected to be located.

The bale was seized as evidence and will likely be destroyed, investigators said.

One thing drug officials and the volunteer agree on: the strange discovery Thursday afternoon is in no way a reflection of the work the food bank does.

In its nearly quarter-century of service, Good Shepherd has become a supplier to more than 470 food pantries and soup kitchens in Maine. Last year, the group distributed more than 9 million pounds of food.

Volunteers sort food from supermarkets and other sources, throwing away the products that cannot be eaten. The rest – clean, fresh and safe – feed an estimated 50,000 people each month.

“You should see the food we’ve unloaded,” the volunteer said. “It really is a blessing.”