Ballast water management

Ballast water management addresses one of shipping’s less obvious environmental impacts: seawater ballast loaded in one region and discharged in another carries organisms — larvae, plankton, bacteria — that can establish themselves as invasive species, with the zebra mussel’s colonization of the North American Great Lakes as the canonical example.

The IMO’s Ballast Water Management Convention (adopted 2004, in force since 2017) requires ships to manage ballast water to the “D-2” performance standard, which in practice means installing an approved ballast water treatment system using filtration combined with UV irradiation or electro-chlorination. The earlier “D-1” standard — exchanging ballast in deep ocean water — served as an interim measure during the phase-in.

Ships must carry a ballast water management plan, a record book, and an international certificate. The retrofit wave through the early 2020s was a significant capital expense across the world fleet, and the United States maintains its own, partly stricter, requirements enforced by the Coast Guard and EPA.