MADISON, Wis. -

Madison police are stepping up their effort to keep synthetic marijuana off store shelves.

Back in January Madison was one of 109 cities that participated in a nationwide initiative called Operation Log Jam. Lt. Brian Ackeret with the Madison Police Department says that's when the Dane County Narcotics Task force began its investigation.

The task force consists of the Dane County Sheriff's Office, UW police and Madison police. Possession of synthetic cannabinoids is illegal under federal and state statues.

During a second round of compliance checks in July, investigators seized 9.75 kilograms from stores throughout the county.

"Over $64,000 in product seized in Dane County in one day, we believe that's just the tip of the iceberg," said Lt. Ackeret.

Officials said five dane county businesses have been caught selling synthetic cannabinoids:

BP 4222 E. Washington Ave.
Mobil 3019 E. Washington Ave.
Shell 950 S. Park St.
Sunshine Daydream 619 State St.
Amsterdam 917 Williamson St.
BP 1525 State St. (Black Earth)

They said all of the materials they confiscated tested positive for illegal chemicals.

Lt. Ackeret says plant leaves are sprayed or dipped in the illegal substance and sold as incense and is not for human consumption. Investigators say it can cause effects similar to marijuana. It retails under different names for about $12.99 to $44.99 a package usually between 1 to 5 grams.

Police are working with UW police and the Dane County Sheriffs Office to help educate store owners.

Shop owners who fail to comply risk fines and time behind bars for selling an illegal substance. The Dane County Narcotics Taskforce is also working with the Drug Enforcement Administration on a case against a specific wholesale dealer. Few details are being released about that pending case.