BOLLES HARBOR, Mich. -- Police confirmed that the mysterious dust found on dozens of homes in Monroe County was fly ash from a Monroe Power Plant.

Monroe County Police said that DTE Energy released a plume of smoke from Monroe Power Plant in Monroe around 7:45 p.m. Monday.

"One of the coal-fired generating units at the Monroe Power Plant shut down automatically and caused a minor release of fly ash from the plant exhaust stack," said DTE spokesman John Austerberry.

"The volume and the duration of the release did not exceed the plant permit limit," Austerberry said.

Witnesses had told police they believed a crop duster accidentally sprayed their homes Monday evening with a substance used to spray crops.

Police confirmed a small plane was flying over the area about the same time DTE released the plume of smoke.

Authorities confirmed the plane was not the cause.

A three-to four-block area in Bolles Harbor was affected.

As a precaution, the Detroit and Washington Federal Bureau of Investigation units and Homeland Security were notified.

A sample of the powder was collected and sent to the Michigan State police crime lab to identify the substance, but preliminary investigations indicate it was coal dust.

DTE said the fly ash does not pose a health threat to residents and they have established a voicemail hot line for the affected residents to call for further information.

DTE asks callers to leave a message with their name and return telephone number so a representative can get back with them.

The hot line number is 734- 384-2139.