About 3 p.m. Monday, a communications watchstander at Coast Guard Station Michigan City, Ind., was notified that people were coming out the water with an oily substance on them at Porter Beach, Ind.
The station directed the reporting source to contact the National Response Center.
Coast Guard Marine Safety Unit Chicago dispatched a response boat to the area, and pollution investigators found no visible sheen.
A helicopter crew from Coast Guard Air Station Traverse City, Mich., was diverted from a training mission to conduct an overflight of the area from the Port of Indiana to Michigan City, Ind., and found no evidence of sheen. They did see a few pollen blooms.
The U.S. Geological Survey has taken water samples, and the results are pending.
Just after 4 p.m., Station Michigan City received a report that the sheen had reached Michigan City.
MSU Chicago is currently on scene investigating, and they have found no sign of sheen. Coast Guard investigators are also reviewing a surveillance video provided by the Port of Indiana and have not noticed any signs of pollution.
The cause of the sheen remains under investigation, and the Coast Guard is working diligently alongside partner agencies to determine any causative factors to see if there is anything that can be done to prevent similar occurrences.