Ballast Water Exchange

Ballast water exchange is the D-1 standard under the IMO BWM Convention, replacing coastal ballast with open-ocean water to cut the transfer of coastal organisms and pathogens between ports. D-1 requires 95% volumetric exchange, or pumping through three times each tank’s volume, performed at least 200 nautical miles from land in water at least 200 meters deep. Exchange relies on the lower survival of coastal species in oceanic salinity and the dilution of the original biota. It is a transitional measure: the BWM Convention’s D-2 performance standard, requiring treatment to fixed organism limits, has superseded exchange-only compliance for the fleet on the implementation schedule.