(1:35 p.m. EST) -- Advocacy groups are going toe to toe over the cruise industry's environmental impact. While Friends of Earth, a nonprofit environmental organization, has released a report critical of the cruise industry, Cruise Lines International Association has responded by questioning the validity of the report, citing arbitrary and faulty measures.

According to the 2012 Cruise Ship Report Card, which is partly based on statistics from as far back as 2010, Disney Cruise Line showed the most improvement and commitment to the environment, while three other cruise lines were given failing grades.

The 2012 report "shows a continued lack of effort on behalf of many cruise lines to pursue ways to reduce their air and water pollution impact on the places passengers take cruises to see," FOE said in a statement released with the report. The mediocre scores that many of the 15 cruise lines and 148 ships received "represent a stagnating trend of environmental responsibility within the industry."

But FOE's report wasn't only full of bad news for the cruise industry. Six lines showed improvement since 2010, though, for most, that simply came from no longer failing.

Disney Cruise Line this year received a grade of "A-," up from a "C-" in 2010.

"Disney's efforts to reduce its air emissions brought it up," according to the Friends of Earth release.

Princess Cruises also showed marked improvement, receiving a "B+", Marcie Keever, an FOE spokeswoman, told Cruise Critic.

"Princess Cruises not only retrofitted nine of their ships to be able to plug into shore power, they've helped ports with funds to update so they can have the shore power available," she said.

Princess also "shaped up" in Alaska, she told Cruise Critic, going from some 30 violations of Alaska's water quality requirements in 2009 to four (all by one ship) in 2010, the most recent data to which Keever said she has access.

When asked why FOE didn't use more recent statistics, Keever said Alaska had not yet provided any for 2011 or 2012 and admitted it's possible there were in fact no violations over the past two years.

"That is a distinct possibility. We did see a drop from the 2009 to 2010 violations, so it is entirely possible. We hope that it is."

Other cruise lines that improved are Carnival Cruise Lines (D+), Celebrity Cruises (C-), Regent Seven Seas Cruises (C) and Silversea (D). Lines that failed are Costa Cruises, Crystal Cruises and P&O Cruises.

But CLIA, an organization that represents the cruise lines in marketing and government lobbying, cautions consumers from taking the FOE report card at face value.

"Consumers should not choose a cruise vacation relying on Friends of the Earth's environmental report card, which, like its previous report cards, lacks basis in fact, science and law," David Peikin, director of public affairs, told Cruise Critic. "The grades assigned cruise lines and their ships are based upon arbitrary, faulty and misleading measures."

For instance, to determine the air pollution reduction grade of a ship, only ships that dock at ports and plug in to shore side power are given a grade above failing, regardless of any other measures the cruise ships and lines might take to increase fuel efficiency and cut down on the amount of fuel burned.

Keever told Cruise Critic that efforts, such as using solar panels, low-energy LED lighting and special hull coatings are "a step in the right direction" but show that these lines are not willing to "go the bigger step like doing shore power or cleaning up the fuel they useā€¦ While it is a good thing, we think they should be taking even bigger steps."

Other environmentally conscious efforts, such as recycling or trash disposal programs of paper, glass, scrap metal, fluorescent lamps, batteries, toner, cooking oil and photo processing chemicals also were not taken into account for purposes of the report.

"The global cruise industry employs practices and procedures that are substantially more protective of the environment than are required by regulation," Peikin said. "All CLIA member lines must meet or exceed all applicable national and international environmental regulations. We advocate practices that fully protect coastal waters wherever we operate and our members have invested extensively to implement a wide range of innovative environmental solutions that reduce air pollution, treat sewage prior to discharge and protect air quality."

--by Dori Saltzman, News Editor