The 216-foot Yorktown ran aground Aug. 25 near Wyandotte, and a tug freed it the next day.
The Coast Guard says there were no injuries, damage or pollution in the grounding of the Cleveland-bound ship.
The agency said Tuesday that its investigation determined the crewmember operating the Yorktown at the time "made serious errors in judgment due to his lack in waterway familiarization and understanding."
It says he also lacked the proper certification for the waters in question.
The Coast Guard says it fined Miami-based V Ships Leisure USA $3,000. The Associated Press left a telephone message Tuesday evening seeking comment from the company.