New rules are now in force to restrict the amount of rubbish which can be discharged at sea.
Maritime New Zealand said the changes mean that previously allowable items such as ropes, fishing gear, cooking oil, packing material, glass, paper and bottles can no longer be thrown into the sea.
Incinerated plastics are also not to be thrown from vessels.
Animal carcasses and some food waste can still be discharged, but vessels must be more than 12 nautical miles from shore.
Further restrictions apply to the discharge of chemical and cleaning agents which are harmful to the marine environment.
Maritime New Zealand says the new rules are designed to reduce marine pollution.