U.S. Customs in Port Huron have seized an estimated $15,000 in fentanyl in eight separate shipments heading across the Blue Water Bridge.

Border protection officials say about 572 grams of fentanyl headed for U.S. cities was found during special operations throughout January.

The shipments were reportedly travelling in Canadian mail trucks and the contents listed for the packages did not match what appeared to be inside.

They were examined in Michigan where each was found to contain a white, rock-like substance which testing showed contained fentanyl and sugar alcohol.

“Our officer’s commitment to serve and protect is constant and this is just one of the ways we are doing our part to stem the opioid crisis impacting our nation,” said Port Director Michael Fox in a statement.

Officials add that if the fentanyl had been further processed and distributed it could have impacted thousands of U.S. citizens with deadly results.