MIAMI (CNN) -- Royal Caribbean Cruise International,the world's second largest cruise line, has pleaded guilty to federal charges stemming from a massive oil-dumping case.

The plea agreement, announced Tuesday in a U.S. District Court, came on the day that the first of two federal trials was scheduled to begin. The agreement encompasses both cases filed by the U.S. Department of Justice, on 11 charges that included oil dumping, falsification of records, obstruction of justice and witness tampering.

"These actions were totally inexcusable. They were wrong, and the company accepts full responsibility," Royal Caribbean President Jack Williams told the court. Later, in a written statement released to the media, the cruise line said: "We deeply regret our role in polluting the marine environment and we are particularly sorry for the attempts to conceal that pollution."

Royal Caribbean has agreed to pay $9 million in fines, $1 million of which will go to a federal program and be used to help preserve reefs in South Florida and Puerto Rico. The settlement is believed to be one of the largest involving a cruise line accused of intentionally polluting the environment.

At sentencing, scheduled for September 16, the cruise line also faces a three- to five-year probationary period during which time it will be scrutinized by an environmental compliance program.

The two federal cases involve incidents with five cruise ships, or half the fleet, dating back to 1993. The U.S. Justice Department had named the following ships as part of its cases: The Sovereign of the Seas, Monarch of the Seas, Song of America, Nordic Prince, and Nordic Empress.

Prosecutors told CNN their evidence against the cruise line included testimony from employees who said they dismantled a system created by the cruise line to bypass required pollution controls. The employees told prosecutors they cut the system into pieces and dumped it into the Port of Miami before a scheduled boarding by U.S. Coast Guard officials.

Prosecutors also had infrared video of a seven-mile-long (11-kilometer) oil slick that came from the Nordic Empress in February 1993. The Coast Guard had suspected the slick was oil, but employees at the time claimed it was hot shower water being disposed of by the ship.

Normally, used oil is kept in holding tanks aboard ship for proper disposal onshore.

Prosecutors said the cruise line kept a phony record book that was referred to by a Norwegian term that translates to "the fairy tale book."