The German operator of a cargo ship detained at a Lake Superior port in Minnesota last year is charged with covering up illegal dumping of oily wastewater.

U.S. Attorney Andrew Luger announced Wednesday that the German shipping company MST Mineralien Schiffahrt was indicted for violating the Act to Prevent Pollution from Ships.

The company is accused of failing to maintain an accurate ship record about the disposal of oil-contaminated waste and presenting falsified records to the U.S. Coast Guard.

The ocean-going M/V Cornelia was detained just outside the Duluth harbor for more than a month while the Coast Guard investigated the alleged discharge of oily water somewhere other than Duluth. The 576-foot, Liberian-flagged ship finally left on Dec. 18.

Company officials did not immediately respond to requests for comment.