<P> Commercial vessels are required to obtain NPDES permits pursuant to Section 402 of the Clean Water Act . Section 312 of the Act prohibits the dumping of untreated or inadequately treated sewage from vessels into the navigable waters of the United States (defined in the act as within 3 miles (4.8 km) of shore). Cruise ships are subject to this prohibition . Commercial and recreational vessels with installed toilets are required to have marine sanitation devices, which are designed to prevent the discharge of untreated sewage . Beyond 3 miles (4.8 km), raw sewage can be discharged . On some cruise ships, especially many of those that travel in Alaskan waters, sewage is treated using Advanced Wastewater Treatment (AWT) systems that generally provide improved screening, treatment, disinfection, and sludge processing as compared with traditional MSDs . AWTs are believed to be very effective in removing pathogens, oxygen - demanding substances, suspended solids, oil and grease, and particulate metals from sewage, but only moderately effective in removing dissolved metals and nutrients (ammonia, nitrogen and phosphorus). </P> <P> States may also establish no - discharge zones (NDZs) for vessel sewage, under section 312 . A state may completely prohibit the discharge of both treated and untreated sewage from all vessels with installed toilets into some or all waters over which it has jurisdiction (up to 3 miles (4.8 km) from land). As of 2017, this designation has been used for 72 areas representing part or all of the waters of 26 states, including a number of inland states . </P> <P> Graywater discharges from large cruise ships are regulated by the 2013 VGP . Graywater discharges from small cruise ships are currently exempt from the EPA Small Vessel General Permit ("sVGP"), due to the Congressional moratorium . </P> <P> Pursuant to a state law in Alaska, greywater must be treated prior to discharge into that state's waters . </P>

Where do cruise ships dispose of their waste