Cruise ships do pose some additional environmental risks compared with other vessels. That's because a large cruise carries thousands of passengers, each of whom produces a personal waste stream that can end up in the ocean. In a recent EPA survey of boats operating in Alaska, cruise ships reported generating an average of 21,000 gallons of sewage a day. Those ships also produced a daily average of 170,000 gallons of graywater—the stuff that drains from sinks, showers, and laundry machines. Graywater can contain detergents, oil, grease, and food waste as well as oxygen-depleting nutrients and various pathogens.
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