MACKINAW CITY, Mich. (AP) — The U.S. Coast Guard says a coolant fluid leak this week from submerged electric cables into the waterway that connects Lake Huron and Lake Michigan may have been caused by a marine vessel.

Ensign Pamela Manns said Friday that the Coast Guard is investigating the cause.

The Coast Guard says about 600 gallons of mineral-based synthetic oil escaped into the Straits of Mackinac, which is between Michigan’s Upper and Lower peninsulas. The two cables are operated by Wisconsin-based American Transmission Company, which has taken them out of service.

Officials say there’s little risk to the public or wildlife because the fluid will be diluted, while heavy shoreline ice should prevent anyone from coming in contact with the oil.