Just days before trial, prosecutors dropped charges against two people accused of intentionally discharging oily water into Lake Huron from a tugboat in 2014.
The oily sheens were spotted by air, east of Cheboygan and east of Alpena. One was 600 feet long. Engineer Jeffrey Patrick and assistant engineer William Harrigan were charged with conspiracy and another crime while aboard a boat called Victory.
At the request of prosecutors, a federal judge in Bay City dismissed the indictment last week. There's no explanation in court documents. A trial was set to start Tuesday.
Messages seeking comment were left for defense lawyers and prosecutors Monday.
A year ago, the U.S. Environmental Protection Agency said the case would send a "strong message" about enforcing laws.
