The cruise industry has received mixed marks over the years for its environmental practices.
But this year, every cruise line got a failing grade for transparency from an environmental group.
Friends of the Earth, which produces an annual environmental report card for the cruising industry, said the entire industry stopped cooperating with the group, refusing to provide information on pollution-reduction technologies.
"By working to stifle the Cruise Ship Report Card, the industry attempted to shield itself from continued scrutiny of its environmental practices," said Marcie Keever, oceans and vessels program director for the group.
In the past, Keever said, the grades have been based on information provided by the cruise lines, plus independent research on the technology used by the ships to treat sewage and whether ships use shoreline power hookups instead of running the ship engines, among other efforts.
This year, the report card was based solely on the group's independent research, she said.
But the trade group for the world's cruise lines said in a letter to Friends of the Earth that its members would no longer cooperate, saying the grading system was flawed.
For example, the letter from Cruise Lines International Assn. said, the environmental group bases grades on whether ships hook up to electrical lines while in port. But such power hookups are not always available, the letter said.
"The FOE report does not advance the public's understanding in a meaningful or objective manner," according to the letter, signed by Christine Duffy, president and chief executive of the Cruise Lines International Assn.
Although the annual report said that the industry, as a whole, is "slowly getting greener," no cruise line received an overall grade higher than a C+.
Disney Cruise Lines was given a C+ grade, while Holland America, Norwegian Cruise and Princess all got C grades from Friends of the Earth. Celebrity Cruises got a D+ while Carnival, Cunard, Regent Seven Seas, Royal Caribbean and Seabourn all received D grades.
Several cruise lines based in Japan and Italy got F grades.