Chicago police officers were surprised to find about one thousand giant marijuana plants growing alongside the Bishop Ford Expressway.

The officers spotted the plants Tuesday while flying over Chicago's far south side in a helicopter.

"The plants are pretty big. They're as big as Christmas trees," Chicago police Lt. Michael Ryle told the Chicago Tribune. "Some of the plants are as tall as 10 feet tall."

Camping equipment and food was found near the plants. Whoever planted the marijuana is still at-large.

Police said the growing operation could have raked in nearly $1 million a year.

Watch video, courtesy of the Associated Press, below: