The Carnival Corporation, the world's largest cruise operator, will plead guilty to seven felony counts related to illegally dumping contaminated waste from Caribbean Princess cruise ships and intentionally trying to cover it up, the US Justice Department said Thursday.

Princess will pay a $40 million penalty – the largest amount ever charged for deliberate vessel pollution – for using a so-called “magic pipe” that allowed ship engineers to bypass the ship’s normal equipment and dump oily waste into the ocean, in addition to other illegal practices.

"Let's be very clear: Princess engaged in exceptionally serious criminal offenses," Assistant Attorney General John Cruden said at a press conference. "It deliberately violated the international law regime designed to make sure that our precious oceans are protected."

It was the British Maritime and Coastguard Agency (MCA) who was first learned of the illegal discharge practices, in 2013, when a newly hired engineer reported witnessing the illegal dumping on the Caribbean Princess through the magic pipe device, while clean salt water ran through the ship’s legitimate equipment to create a false digital record.

British officials informed the US Coast Guard, which began an investigation into the cruise ship’s practices once it arrived in New York. In response to the investigation, the ship’s chief engineer and senior engineer removed the magic pipe, and directed those who worked under them to lie, according to the Justice Department.

The investigation ultimately found that the Caribbean Princess and four other Princess ships – the Star Princess, Grand Princess, Coral Princess and Golden Princess – had been using illegal methods as far back as 2005. One Aug. 2013 incident alone discharged 4,227 gallons just 23 miles off the coast of England.

"This shows just how well the UK and US can work together on these kind of cases," Jeremy Smart, the head of enforcement at the Maritime & Coastguard Agency of the United Kingdom, said in a statement from the DOJ. "It also sends a clear message to the industry that this kind of pollution practice will not be tolerated anywhere in the world. It also shows that we will always take any information we are given by those who report such practices to us very seriously and will act upon it."

In addition to the $40 million fine, ships from eight Carnival-owned lines will be monitored by the Environmental Compliance Program for five years.

"We are extremely disappointed about the inexcusable actions of our employees who violated our policies and environmental law when they bypassed our bilge water treatment system and discharged untreated bilge water into the ocean," Princess said in a statement. "Although we had policies and procedures in place, it became apparent they were not fully effective."

Princess has said it cooperated with the DOJ and Coast Guard's investigation, USA Today reports. It has also launched its own investigation, which found other illegal practices on some ships, and has upgraded much of its equipment, and increased the power of ships' environmental officers.

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"Our hope is that all companies abide by regulations that are in place to protect our natural resources and prevent environmental harm," Wilfredo Ferrer, the US attorney for the Southern District of Florida, said in a statement. "Today's case should send a powerful message to other companies that the US government will continue to enforce a zero tolerance policy for deliberate ocean dumping that endangers the countless animals, marine life and humans who rely on clean water to survive."

This report includes material from Reuters.