MARPOL Annex IV

MARPOL Annex IV prevents pollution by sewage from ships. It prohibits discharge of untreated sewage except at more than 12 nautical miles from the nearest land, allows discharge of comminuted and disinfected sewage at more than 3 nautical miles, and permits discharge from an approved sewage treatment plant nearer to shore. Ships of 400 GT and above, and smaller ships certified to carry more than 15 persons, on international voyages must carry an approved treatment plant, holding tank, or discharge connection and an International Sewage Pollution Prevention Certificate. The Baltic Sea is a special area with stricter passenger-ship rules.