Cruise ships generate sewage, greywater, hazardous wastes, oily bilge water, ballast water, solid waste, and air pollutants. If released without proper treatment, these wastes can put pathogens, nutrients, and toxic substances into the environment that could threaten human health and aquatic life. Cruise ships represent a small portion of the international shipping industry, and the waste streams described here are not unique to them. But cruise ships and their passengers and large crews generate more than average amounts of sewage, greywater, and solid waste. They may also have an outsized effect on the subset of ports and coastal areas that see much cruise-ship activity.