The phrase “en route” within the MARPOL regulation appears simple, yet its interpretation plays a crucial role in determining when ships may legally discharge certain wastes at sea, and its meaning can vary significantly across its different annexes and jurisdictions.“En route” in MARPOLMARPOL (International Convention for the Prevention of Pollution from Ships) is the primary international treaty aimed at reducing pollution of the marine environment by ships from both accidental and operational causes. The table below outlines the MARPOL discharge requirements for each Annex in relation to references to “en route”, subject to certain exceptions, areas and local regulations.