Cruises are becoming more and more popular, with around 20 million passengers per year now enjoying holidays on board luxury ( 奢侈的 ) ships. More people see a cruise as the perfect way to sit back and do nothing, and enjoy time off work. But what is the effect on the environment of this trend?

    Although it usually takes less energy for a vehicle to move through water than over land, cruise ships are often massive, with the biggest ones carrying up to 6,000 passengers. Moving such large vehicles requires huge engines which bum as much as 300,000 litres of fuel a day. One scientist has calculated that cruise ships create as much pollution as 5 million cars going over the same distance. Because they are out at sea, they also burn dirtier fuel that isn't allowed on land. Unfortunately, no government has control over the amount of air pollution out at sea. Cruises also produce huge amounts of rubbish, and cruise ships aren't usually good at recycling. Waste water from showers and toilets is usually poured directly into the sea - as much per day as from a small town. Waste food from restaurants isn't put into the sea, but still causes problems when brought back to the land.

    Cruise ships also cause difficulties in the cities where they stop. Popular destinations can get five or six ships per day, with thousands of tourists at a time. Good for restaurants? No. Restaurant owners complain that the visitors look around for a few hours and then return to their ship to eat. What's more, the crowds can put off other tourists, who complain that the streets are too busy.

    Some towns have banned (禁止) cruise ships or put a limit on the number that can stop at the same time. People who care about the environment worry that as the cruise industry continues to grow, so will the issues for our planet.