A brief history

The BWM Convention — formally the International Convention for the Control and Management of Ships’ Ballast Water and Sediments — has a long history. IMO adopted it in 2004, but it entered into force on 8 September 2017. Finland triggered that milestone on 8 September 2016. As the 52nd ratifying state, it pushed total represented tonnage to 35.14%, clearing the required 35% threshold.
Why does ballast water need managing at all? Ships take on ballast water for stability when they carry little or no cargo. That water can contain thousands of aquatic organisms — algae, bacteria, invertebrates, fish larvae. When the ship pumps it out at a distant port, those organisms enter an ecosystem where they did not evolve. Some become invasive. The ecological damage can be severe and lasting.

Two standards

The Convention created two management standards.

The D-1 standard is transitional. It requires ships to exchange ballast water at sea. The ideal location is at least 200 nautical miles from land in water at least 200 metres deep. Coastal organisms rarely survive in deep-ocean conditions, so the replacement water poses far less risk. Where those distances are unachievable, ships may exchange at 50 nautical miles from land in 200-metre water, or in a designated exchange area.

The D-2 standard is the definitive requirement. It sets numerical limits on the organisms and microbes ships may discharge in ballast water:
— fewer than 10 viable organisms per cubic metre at 50 micrometres or larger;
— fewer than 10 viable organisms per millilitre between 10 and 50 micrometres;
— fewer than 1 cfu of Toxicogenic Vibrio cholerae per 100 ml;
— fewer than 250 cfu of Escherichia coli per 100 ml;
— fewer than 100 cfu of Intestinal Enterococci per 100 ml.

Meeting these limits demands an onboard Ballast Water Treatment System (BWTS), type-approved by the flag Administration.

Where does compliance stand today?

Since 8 September 2024, every ship in international traffic must meet D-2. The phased schedule linked to IOPP renewal surveys has run its full course. D-1 alone no longer suffices for vessels on international voyages.
Every vessel subject to the Convention must carry a Ballast Water Management Plan (BWMP) and a Ballast Water Record Book (BWRB). Two recent IMO amendments update the record-keeping requirements. Resolution MEPC.369(80) introduced a new BWRB form, mandatory from 1 February 2025. Resolution MEPC.383(81), in force from 1 October 2025, permits electronic BWRBs — but only with flag Administration approval. Ships using an electronic BWRB must carry a ship-specific declaration confirming compliance with MEPC.372(80). PSC inspectors check BWRB entries closely; deficient records rank among the most frequently cited violations

IMO is also reviewing the Convention itself. The Experience-Building Phase (EBP), running since 2017, collects operational data from ships worldwide. Based on that data, MEPC may adopt a package of amendments in 2026. Those amendments could revise D-2 thresholds, testing protocols, or other requirements. Operators should monitor this process.

Vessels trading in the Baltic Sea

Ships sailing between two Baltic ports do not need to exchange ballast water. The Baltic Sea has no designated exchange area. Its shallow depths and limited size make open-sea exchange impractical on most routes. Ships entering from the North Sea face a similar position. The intra-North Sea exchange area covers only intra-North Sea traffic. A vessel entering the Baltic from the North Sea does not cross an applicable area.

Ships arriving from outside both seas — from the Atlantic, for example — must perform a D-1 exchange before entering the Baltic. They should do so as early as possible on the approach. Where a compliant exchange area is unreachable, the master must apply to the Local Maritime Office (Polish: Urząd Morski) before arrival. The application must explain why compliance is impossible. The office can authorise a departure from standard requirements. Vessels that receive an approval — or a denial — must record the outcome in the BWRB. With prior authorisation, operators may arrange commercial ballast water disposal ashore.

The Baltic Sea poses a particular ecological challenge. Its semi-enclosed geography, low salinity, and reduced biodiversity make it highly sensitive to invasive species. Limited water exchange with the North Sea means contaminants and non-native organisms persist far longer than in open-ocean environments. HELCOM coordinates regional BWM implementation across Baltic states. Risk assessments using the Joint Harmonised Procedure found that over 97% of Baltic and North-East Atlantic shipping routes carry a high species-introduction risk. D-2 compliance is not a formality for Baltic operators — it is a genuine environmental necessity.

Polish ports in practice

Poland has ratified the BWM Convention, and port State control inspections follow IMO standards. PSC officers check for a valid International Ballast Water Management Certificate, a current BWMP, and a correctly maintained BWRB. Since February 2025, inspectors also verify that the BWRB follows the MEPC.369(80) format.
If a vessel’s BWTS malfunctions and it cannot discharge compliant ballast water, the master should contact the Local Maritime Office without delay. Commercial ballast water reception facilities exist at major Polish ports. Using them requires advance coordination through the port agent. Any non-standard discharge must appear in the record book, along with the circumstances and any approvals received. A vessel that discharges non-compliant ballast water without authorisation faces detention and significant fines.

See also:

https://www.imo.org/en/mediacentre/hottopics/pages/implementing-the-bwm-convention.aspx