Carnival Corp has been ordered to pay a $20m fine for violating a five-year probation tied to environmental wrongdoing over several years.

The world's largest cruise company reached the tentative agreement today with federal prosecutors as punishment for polluting the ocean for years after vowing to stop, Associated Press reports.

Carnival has served two years of the five-year probation as part of a $40m settlement for illegally dumping oil into the ocean from its Princess Cruises ships for eight years and lying about it to US authorities.

While on probation, Carnival and its subsidiary cruise lines tried to avoid unfavorable findings by preparing ships in advance of court-ordered audits and falsifying records.

The New York-listed company also dumped plastic garbage into the ocean and illegally discharged gray water into Glacier Bay National Park in Alaska.

The company also has tried to lobby the US Coast Guard through a back channel to change the terms of the settlement, prosecutors allege.

The company has acknowledged these incidents, according to court filings.

The proposed settlement was signed by Carnival Chairman Micky Arison, billionaire-owner of the Miami Heat, AP reports.

Both Arison and chief executive Arnold Donald were ordered to appear in court for the hearing.

Carnival must also pay $1m a day if it does not come up with an improved compliance plan by 13 September and 9 October.

Seitz in April threatened to temporarily block Carnival from docking at US ports for violating the probation.

Two Bahamian environmentalists and a fisherman from Alaska on Friday filed a request to delay any decision by two weeks so that could look at Carnival's record and submit testimony.

'New initiatives'

"Today the court approved our agreement with the Department of Justice — setting forth new initiatives, improved procedures, additional training and significant investments to ensure we have the strongest and most sustainable environmental compliance program possible," Carnival said in a statement.

"Carnival Corporation remains committed to environmental excellence and protecting the environment in which we live, work and travel. Our aspiration is to leave the places we touch even better than when we first arrived."

'Slap on the wrist'

The $20m fine does not come close to the punishment that Carnival should receive for its repeated offences against Mother Nature, said Stand.earth, a US-based environmental group leading a Cleanup Carnival campaign.

"The communities and individuals impacted by this recidivist felon’s environmental crimes ended up with more empty words and another back room deal that cannot even be characterized as a slap on the wrist for a multi-billion dollar international corporation," senior shipping campaigner Kendra Ulrich told TradeWinds.

"Today’s ruling was a betrayal of the public trust and a continuation of the weak enforcement action that has allowed Carnival to continue profiting on selling the environment while their ships contribute to the destruction of the fragile ecosystems it visits.”