Garbage and Sewage
Garbage and sewage can both cause problems at sea. The sea can be polluted from a ship's garbage when the ship's crew breaks the international rules and regulations. This happens when garbage is thrown overboard and not stored on the ship in the special containers provided for offloading garbage in port.
Sewage must be treated in specially provided sewage treatment tanks. Once treated it is safe to be pumped overboard. However, pumping untreated sewage overboard in some areas is prohibited by law.
Marine pests can be carried in a ship's ballast water. If a ship takes on water in a port on one side of the world and realeases the ballast water in a different marine environment, the animals in the water can take over the new environment.
Ships must prevent or reduce the chance of this happening. Ships carrying ballast water are required to either exchange their ballast water for new ballast water while sailing to their next port. Alternatively, he ship could treat the ballast water on board with a special system designed to kill any marine pests.
For more information on marine pests go the AUSMEPA education program, Marine Pests & Threats at www.ausmepa.org.au/pests/flash.html