An environmental-advocacy group graded 16 cruise lines on how well they limit pollution. Every Carnival cruise line they graded got an 'F.'

Joe Skipper/Reuters

Carnival's Carnival Ecstasy ship.

• The environmental-advocacy group Friends of the Earth graded 16 cruise lines on how well they limit pollution from their ships.
• The cruise lines were evaluated on how they treat their sewage, the steps they've taken to limit air pollution at ports, whether they follow water-pollution rules in Alaska, and the quality of information they provided about their environmental practices to Friends of the Earth.
• Disney Cruise Line was the only cruise line to receive an overall grade above C-.
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Most cruise lines do a poor job of limiting the damage they do to the environment, according to a new study from the environmental-advocacy group Friends of the Earth.

The group graded 16 cruise lines based on how they treat their sewage, the steps they've taken to limit air pollution at ports, whether they follow water-pollution rules in Alaska, and the quality of information they provided about their environmental practices to Friends of the Earth.

Read more: Carnival, Royal Caribbean, and Norwegian Cruise Line are in a fierce battle for domination in the cruise industry - here's how they stack up

Disney Cruise Line was the only cruise line to receive an overall grade above C-. All cruise lines owned by Carnival Corp automatically received failing grades due to their violation of a settlement related to a 2017 conviction for improper waste disposal.

Here's how the 16 cruise lines fared, from best to worst.