Ballast Water Management Convention

The International Convention for the Control and Management of Ships' Ballast Water and Sediments addresses a serious environmental problem created by an everyday operational necessity. Ships take on seawater as ballast to stay stable and safe when lightly loaded, and discharge it when they load cargo. That water contains living organisms (larvae, plankton, bacteria and small marine life) which can be carried across the world and released alive in a new region, where they may become invasive species that damage native ecosystems, fisheries and infrastructure. The convention, developed by the IMO, exists to break this chain of transfer.

The convention sets two standards. The D-1 standard is ballast water exchange, whereby a ship replaces the coastal water in its tanks with open-ocean water far from land, on the basis that mid-ocean organisms are unlikely to survive in a coastal environment and vice versa. The more demanding D-2 standard is a treatment standard, limiting the number of viable organisms that may be discharged, and it is met by installing an approved ballast water treatment system that typically filters the water and then disinfects it using ultraviolet light or chemical treatment. Ships are transitioning from exchange to treatment, so that in due course all ships must meet the D-2 standard.

Every ship must carry a ballast water management plan setting out how it complies, keep a ballast water record book documenting each operation, and hold an international certificate. Compliance is checked by flag states and by Port State Control, which can sample discharges and detain non-compliant ships. Installing treatment systems has been a major undertaking for the world fleet, and choosing and operating them reliably in varied water conditions has been a real engineering challenge. The convention is a landmark in protecting the marine environment from one of the most damaging consequences of global shipping.