Think your cruise ship experience is squeaky clean? Think again. The Friends of the Earth has just released its second-annual Cruise Ship Environmental Report Card, and it's not all pretty.

One-hundred-thirteen ships on 11 major cruise lines were rated on four criteria -- air pollution reduction, water quality compliance in Alaska, the ease of finding environmental information on a line's website and sewage treatment.

Now, it's that last item that caught my attention. Did you ever wonder what happens to the contents of your toilet when you flush it aboard a cruise ship? I was sure there had to be some sort of tank that catches all that stuff, like in a Winnebago, but that's not always the case. Apparently, what you flush can be dumped untreated directly into the ocean if the ship is at least three 3 nautical miles from shore. Friends of the Earth says that means fecal matter, bacteria, viruses, pathogens, nutrients, hazardous waste and pharmaceuticals can go right into the water, where it can impact human and aquatic life. The group cites a U.S. EPA estimate that a "3,000-person cruise ship generates 210,000 gallons of sewage weekly — enough to fill 10 backyard swimming pools, and 1 million gallons of graywater—another 40 swimming pools full of waste." Blech!

So, which cruise line got straight Fs? That would be Crystal Cruiselines (though water compliance wasn't a factor, since it doesn't sail to Alaska).

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In fact, all but Holland America, Norwegian and Princess got at least one F.

To see the full report card, visit the FOE website.