From D-1 exchange to D-2 treatment
The convention's first tool was D-1, ballast water exchange. Coastal ballast is replaced with open ocean water, generally at least 200 nautical miles from the nearest land and in water at least 200 metres deep, with a reduced distance permitted where that is not possible. The logic is that open ocean organisms rarely survive in ports. Exchange was always an interim measure, dependent on route geometry and weather. The end state is D-2, a numerical discharge standard that limits viable organisms by size class and sets limits for indicator microbes. Meeting D-2 requires an approved ballast water management system, typically filtration combined with UV or electro chlorination, type approved under the BWMS Code. Regulation B-3 phased the transition through IOPP renewal surveys, with a backstop. All ships had to meet D-2 by 8 September 2024. That date has passed, so D-2 is now the operative standard across the fleet and D-1 is no longer a compliance route for ships in scope.
The paperwork that travels with the water
Every ship in scope carries an approved Ballast Water Management Plan, an International Ballast Water Management Certificate and a Ballast Water Record Book documenting every uptake, treatment, exchange and discharge. Two separate amendments changed the record keeping, and they are often confused. Resolution MEPC.369(80), adopted on 7 July 2023 and in force from 1 February 2025, replaced the form of the Ballast Water Record Book with a coded structure using operation codes A to H, modelled on the Oil Record Book. Resolution MEPC.383(81), adopted on 22 March 2024 and in force from 1 October 2025, deals with electronic record books and makes the approval and declaration requirements for them mandatory. Electronic record books themselves were already permitted under regulation B-2 before either amendment. Both changes were a direct response to how often inspectors found entries vague or irreconcilable. The convention also carries an honest feedback loop. An experience building phase gathered data on how systems perform in real service, and that data has fed a review. At MEPC 84, held from 27 April to 1 May 2026, the Committee formally closed the experience building phase and adopted the 2026 G4 Guidelines on ballast water management and the development of ballast water management plans. It also approved a further set of amendments to the convention for adoption at MEPC 85, covering challenging water quality, contingency measures where a system cannot deliver the standard, maintenance records for the treatment system in the record book, and survey and commissioning testing requirements. The Committee confirmed its intent that the revised convention and the revised BWMS Code enter into force together. As at August 2026 those amendments are approved but not yet adopted, so they should be tracked rather than planned around as settled law.
Where compliance actually fails
The operational failure modes are consistent. The treatment system is bypassed or inoperable and the fact is not recorded or reported. Crews cannot operate the system confidently, particularly after a crew change. Record book entries do not reconcile with tank soundings and voyage data. Contingency measures, meaning what to do when the system fails before a discharge, are neither planned nor understood. Port States have limited patience for an explanation that the system was broken when there are no contemporaneous records, no notification and no plan. The 2025 campaign confirmed the pattern. It ran from 1 September to 30 November 2025 across both regions. In the Tokyo MoU region the campaign window covered 9,244 Port State Control inspections, of which 6,930, or 74.96 per cent, applied the campaign questionnaire. Among the ships inspected under the campaign there were 184 detentions in total, of which 30 were detentions on the campaign topic itself. The Tokyo MoU also reported ballast water related deficiencies at roughly three times the previous year's level, with the most common finding concerning the proper operation of the treatment system. Port State Control now treats ballast water as core business, not a specialty topic.
Running it well
The ships that stay clean on ballast water treat the treatment system as critical machinery rather than as an installed inconvenience. Planned maintenance is honoured. Spares are carried. Crews are drilled on both normal operation and failure response. Every anomaly is logged, reported and followed through. The convention's demands are ultimately modest: treat the water, keep honest records, have a plan for failure. It is unforgiving of improvisation.