A German shipping company whose vessel was detained offshore from Duluth for six weeks late last year has been slapped with $1 million in penalties after its owners pleaded guilty to dumping oily wastewater into the Great Lakes.

Officials of the company, MST of Schnaittenbach, Germany, pleaded guilty on Tuesday before U.S. District Judge Joan N. Ericksen in U.S. District Court in Minneapolis, according to a news release from the U.S. Attorney’s Office for the Minnesota district.

The Coast Guard held MST’s oceangoing freighter Cornelia in the harbor from early November until Dec. 18, when it finally was allowed to depart.

According to the news release, the Cornelia’s crew discharged oily wastewater overboard at least 10 times from February to October 2015, and its chief engineer intentionally failed to record the discharges in its record book. That included at least one incident while the vessel was in the Great Lakes.

The guilty plea was to violation of the Act to Prevent Pollution from Ships.

MST will be required to pay a $800,000 criminal fine to the United States in addition to a $200,000 community service payment to support the protection and preservation of Lake Superior and its watershed, according to the news release.

The company also will serve a three-year probationary period during which it must commit no further violations and implement an environmental compliance plan for all of its vessels that call on ports or places in the U.S.