WASHINGTON (CNN) -- Royal Caribbean Cruises was sentenced Wednesday to pay an $8 million criminal fine for dumping oil and lying to the U.S. Coast Guard about it.

The sentence against the world's second largest passenger cruise line was delivered in a federal court in Puerto Rico. It was in addition to the $1 million fine against the cruise line levied last month in a Miami court.

The two cases were part of a plea bargain by Royal Caribbean that includes five years of probation, during which time it will be monitored for its environmental conduct.

In June, the cruise line pleaded guilty to eight felony counts in a pretrial agreement with prosecutors on cases brought against it in Florida and Puerto Rico.

According to the Justice Department, even after that agreement, there were new violations in July that involved tampering with oil limiting sensors and false statements in a log book aboard the Nordic Empress cruise ship.

Royal Caribbean said it reported the July incident to the government itself after an employee noticed two engineers tampering with equipment.

"We took it very seriously. The two engineers involved have been fired," said Lynn Martenstein, a spokeswoman for the cruise line. She said an environmental plan is being developed with the government for the court's approval by December 15.

"Royal Caribbean's crimes, including dumping oil into our oceans, lying about it, and trying to cover it up by obstructing justice, are serious offenses that require serious punishment," said Assistant Attorney General Lois Schiffer.

The investigation of the cruise line began in 1994. In June, the cruise line admitted that its crews routinely dumped oil bilge, kept dummy logs called "fairy tale" books by the crew and disassembled illegal sewage pipes bypassing cleaning devices in a conspiracy to hide the illegal practices.

Under the plea agreement, Royal Caribbean will pay another $1 million for environmental projects in the Puerto Rico and South Florida areas. The cruise line also will present regular environmental reports and independent audits to the government under its probation requirements.

"This case gives fair warning to cruise lines and other corporations which seek to maximize profits by illegally discharging wastes at sea," said Steve Herman, assistant administrator at the Environmental Protection Agency.

CNN Correspondent Terry Frieden and Reuters Limited contributed to this report.