Princess Cruise Lines Ltd. was sentenced Wednesday to pay $40 million, the largest-ever fine for deliberate vessel pollution, according to the U.S. Justice Department.

The sentence for the Santa Clarita-based cruise line also requires that Princess remain on probation for five years during which time its ships must implement an environmental compliance plan.

According to court papers, the ship Caribbean Princess had made illegal discharges since 2005. In August 2013, it discharged about 4,227 gallons off the coast of England within the country’s Exclusive Economic Zone. At the same time as the discharge, engineers ran clean seawater through the ship’s monitoring equipment in order to conceal the criminal conduct and create a false digital record for a legitimate discharge.

The case against Princess included illegal practices on five ships – Caribbean Princess, Star Princess, Grand Princess, Coral Princess and Golden Princess.

The case was investigated by the U.S. Coast Guard.