Cruise ships are designed with serious comfort in mind, so they have a lot of amenities and a lot of staff to oversee those amenities for the as many as 3,000 passengers. These thousands of passengers are spread out over the ship’s multiple levels called decks.

These cruise ships are also relatively easy to “contain” that is, it’s easy

to control and limit access to the ships. When a ship is in port, passengers and crew can only enter through one or two controlled access points, where ship’s security personnel can check IDs, manifests and such.

Large cruise ships are required to follow strict environmental regulations that ensure that treated sewage and waste water from showers, sinks and kitchen galleys are discharged properly at designated offshore perimeters. In fact, cruise line waste management is so highly regarded that cruise lines are often consulted by state governments on pollution abatement and sewage control.