What does a No Discharge zone restrict in boating?

Answer 1

A no discharge zone is one where no vessel may discharge anything into the water. This includes sewage, grey water (water from sinks) and bilge water. In these areas the bilge pumps should be taken out of the automatic mode so that there is no oily bilge water discharges.

Bilge pumps are for the safety of a vessel you should not turn them off. as regards to oil in the bilge water this is down to the lack of another safety feature i.e a drip tray under the engines the purpose of which is to capture any oil and stop it from entering the bilges and spreading throughout the vessel. If you were to have a fire on board you should contain it to the smallest possible area for it to be extinguished , if you have oil spread throughout the bilges a fire will spread throughout the boat. If this is the case and you have oil in the bilges a thorough cleaning of the bilges and containment of any oil leaks is dangerously over due.

I remember a couple who motor sailed to Norway tied the boat up and went ashore for about 30 minutes when they got back to the boat it was slowly sinking. This was caused by the sterngland leaking slightly after the engine was switched off. Had the bilge pumps been switched off at the time the boat would have sunk to near deck level.